Ab Initio Calculation

A study of the intermolecular potential-energy surface ͑IPS͒ and the intermolecular states of the perprotonated and perdeuterated benzene-He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two-to four-body atom-atom terms is obtained. This IPS, and two other Lennard-Jones atom-atom surfaces from the literature, are each employed in dynamically exact ͑within the rigid-monomer approximation͒ calculations of Jϭ0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational transitions are also calculated for each of the three surfaces. The calculated results are compared with experimental results reported herein pertaining to intermolecular Raman spectra of benzene-He. The calculated rotational constants are compared with experimental values from the literature. The fitted IPS of this work leads to calculated observables that match the experimental results very well. The IPSs from the literature are not as successful, specifically in regard to the intermolecular Raman spectra.

The x-ray Faraday effect at the L 2,3 edges of the 3d ferromagnets Fe, Co, Ni and of Fe 0.5 Ni 0.5 alloy is studied both theoretically and experimentally. We perform ab initio calculations of the x-ray Faraday effect on the basis of the local spin-density approximation and we adopt the linear-response formalism to describe the material's response to the incident light. Experimental x-ray Faraday rotation and ellipticity spectra are measured with linearly polarized soft-x-ray synchrotron radiation at BESSY, Berlin. The measured x-ray Faraday rotations are remarkably large, up to 2.8ϫ10 5 deg/mm, which is more than one order of magnitude larger than those observed in the visible range. From the measured Faraday spectra we determine the intrinsic dichroic contributions to the dispersive and absorptive parts of the refractive index, and compare these to ab initio calculated counterparts. The theoretical dichroic spectra are in good qualitative agreement with the experimental data. The inclusion of the spin polarization of the core states leads to a small, yet non-negligible, improvement of the theoretical dichroic spectra. Our results illustrate that the many-particle x-ray excitation spectrum can be sufficiently well approximated by the Kohn-Sham single-particle spectrum. From the computed magneto-x-ray spectra we determine, using the sum rules, the orbital moments, which we compare to the exact orbital moments.

The existence of the x-ray magneto-optical Voigt effect is demonstrated. By means of polarization analysis the Voigt rotation and ellipticity of linearly polarized synchrotron radiation are measured at the Co L 3 edge upon transmission through an amorphous Co film. The observed x-ray Voigt rotation is about 7.5 ± ͞mm. On the basis of ab initio calculations it is shown that the x-ray Voigt effect follows sensitively the amount of spin polarization of the 2p core states. Therefore it provides a unique measure of the spin splitting of the core states.

We present experimental magneto-optical (MO) Faraday rotation data obtained with linearly polarised soft X-ray synchrotron radiation at the 2p-3d resonance in Fe films. The dichroism of the dispersive and absorptive parts of the refraction index are compared with ab initio calculations based on the local approximation to spin-density functional theory.

An approach based on statistical thermodynamics and ab initio calculations to predict properties of materials composed of different types of atoms is presented. The key point of what the authors called the "Hakoniwa" method, is to take into account all possible structural supercells constructed by the fixed number of atoms of each species according to the composition of the target material. The conservation of the total number of atoms enables calculating the average value of a material property for a given temperature by applying statistical thermodynamics to the material property values obtained for each of

We have parameterized the various interactions between Cu adatoms on Cu(1 1 0) using density-functional theory based ab-initio calculations. Our results indicate that in addition to pair interactions, 3-adatom and 4-adatom interactions of significant strengths are present in this system. This further stresses the importance of multi-site interactions in constructing a complete lattice-gas picture. Even though adding these multi-site interactions leads to good convergence in interaction energies, we find that some multi-site interactions are very sensitive to adatom relaxations. This makes the application of a simple lattice-gas picture inadequate for such surfaces. We also parameterize adatom interactions on this surface using the recently developed connector model. The connector model parameterization is as efficient as the parameterization using lattice-gas model. Further, we present diffusion barriers for nearest-neighbor (NN) and next-nearest-neighbor (NNN) hops on this surface.

Using a van der Waals density functional (vdW-DF) [Phys. Rev. Lett. 92, 246401 (2004)], we perform ab initio calculations for the adsorption energy of benzene (Bz) on Cu(111) as a function of lateral position and height. We find that the vdW-DF inclusion of nonlocal correlations (responsible for dispersive interactions) changes the relative stability of eight binding-position options and increases the binding energy by over an order of magnitude, achieving good agreement with experiment. The admolecules can move almost freely along a honeycomb web of "corridors" passing between fcc and hcp hollow sites via bridge sites. Our diffusion barriers (for dilute and two condensed adsorbate phases) are consistent with experimental observations. Further vdW-DF calculations suggest that the more compact (hexagonal) Bz-overlayer phase, with lattice constant a = 6.74 Å, is due to direct Bz-Bz vdW attraction, which extends to ∼ 8 Å. We attribute the second, sparser hexagonal Bz phase, with a = 10.24 Å, to indirect electronic interactions mediated by the metallic surface state on Cu(111). To support this claim, we use a formal Harris-functional approach to evaluate nonperturbationally the asymptotic form of this indirect interaction. Thus, we can account well for benzene self-organization on Cu(111).

A general all-atoms force field (FF) for atomistic simulation of low molecular weight hydrofluorocarbons (HFCs) was developed using state-of-art ab initio calculations and empirical parameterization techniques. The FF is based on ab initio quantum mechanical calculations for the valence parameters and on molecular dynamics (MD) simulations for the tuning of the Lennard-Jones (LJ) parameters describing the dispersion forces. Validation of the proposed FF has been made versus intramolecular properties of isolated molecules, vibrational spectra, and intermolecular properties of liquid state molecules such as cohesive energy, enthalpy of vaporization and density for molecules of interest. The reported results show that the present force filed enables accurate and simultaneous prediction of structural, conformational, vibrational and thermophysical properties for low molecular weight HFCs in isolation and in condensed phase. Detailed results of the parameterization and validation are reported.

These two polymorphs are wurtzite and zinc-blende (also known as sphalerite). In which Wurtzite has a hexagonal structure, while zinc-blende structure (ZBS) is cubic. The zinc chalcogenides are one compound of ZBS which have much interesting studies due to importance of semiconductor properties. The nature and physical properties of II-VI groups of this compound have been studied by modifying of VTSM model. This paper explains only Debye temperature variations at room temperature have been calculated for zinc chalcogenides using VTRSM model.

This thesis investigates the spectroscopic and thermodynamic properties of molecular liquids. To this end, we use techniques of quantum chemistry and modeling to do computational simulation. To simulate the thermodynamic properties and molecular flexibility it was used Classical Simulation (Monte Carlo and Molecular Dynamics). To reproduce the electronic properties it was used Quantum Chemistry methods (post-HF and DFT). The polarization effect was introduced through the Sequential Monte Carlo / Quantum Mechanics Method and polarizable force fields. It is presented an overview of these techniques in the appendix. This work is divided into three parts. In the first part is obtained spectroscopic and structural properties of phenol and water (1+1 and 1+2) and phenol and ethanol (1+1) clusters. The vibrational modes (intra and intermolecular) and binding energies are calculated. The structural results and the solvatochromic deviations are consistent with experimental data and theoretical expectations (for different clusters). In the second part is performed the simulation of phenol in water using the S-MC/QM protocol, followed by the calculation of the electronic spectrum. It is presented the study of hydrogen bonding and the different contributions which determine the solvatochromic deviation in solution. So, it is made the simulation of phenol in ethanol using molecular dynamics and the polarizable and flexible force field AMOEBA. The thermodynamic properties of the simulation are in excellent agreement with theoretical expectations and experimental data. This is surprising given the fact that the model is not parameterized empirically. Finally, it is detailed the work on supercritical water. It has been performed hundreds of simulations in order to obtain the critical point of the model AMOEBA. Isotherms are presented as well as the parameters of the equation of state which determine the behavior of the model in that region. This document samples the acquired knowledge of the student in different aspects of computational physics, from the technical side, the various models and theoretical approaches used in simulation and the ability to apply this knowledge to problems of physical interest, which resulted in two published articles and other two are in preparation.

Presented is a study of uncompensated magnetization in antiferromagnets performed by SQUID and VSM magnetometry, and polarized neutron reflectometry. This uncompensated magnetization is observed and studied as a function of temperature and cooling conditions. Uncompensated magnetization is found close to the top surface of the antiferromagnet (interface with the ferromagnet) and also in the "bulk" of the antiferromagnetic film. It has been established that this uncompensated magnetization plays crucial role in exchange bias. To understand the origin of uncompensated magnetization, ab initio calculations are performed.

The absorption spectrum of Mg I vapour between 2000 and 700 ņ has been reinvestigated, using the continuum emitted by the Bonn 500 MeV electron synchrotron as the source of background radiation. Extensions to the double excitation spectrum of the valence shell have resulted and are compared with recent data obtained by electron impact spectroscopy. Ab initio calculations of the doubly excited configurations have been extended to high series members, and the transition from LS to jj coupling is shown to be responsible for the appearance of a 1 S 0 - 3 P 1 series not previously detected by photoabsorption.

The lattice dynamics of zinc-blende ͑ZB͒ CuBr and CuI is studied as a function of pressure using density functional linear-response theory. A pressure-induced soft transverse acoustic ͑TA͒ phonon mode is identified for both compounds. Each compound shows a different pressure-induced phonon softening behavior. A TA phonon branch softens along the ͓ 0͔ direction in CuBr, resulting in a phase transition from a ZB phase ͑CuBr-III͒ to a tetragonal phase ͑CuBr-IV͒. A softening TA phonon mode at the zone boundary L point in CuI may induce a phase transition from a ZB phase ͑CuI-III͒ to a rhombohedral phase ͑CuI-IV͒, although the phonon softening towards zero frequency in CuI is superseded by a first order phase transition occurring at 1.74 GPa. Possible phase transition paths are presented for both compounds.

Auger-photoelectron coincidence measurements for polarized targets are theoretically considered. We present a general expression for the cross section of sequential double photoionization of polarized atoms within the two-step model. Linear magnetic and alignment dichroism in coincidence experiments is discussed in more detail. For illustration, we made ab initio calculations based on the multiconfigurational Dirac-Fock theory for the 4d photoionization of atomic Sn followed by N-OO Auger decay.

Molecular-dynamics simulations were used to calculate the Gibbs free energy on the entire compositional range of gold-nickel alloys described with a set of embedded atom potentials available in the literature. Thermodynamic integration and switching Hamiltonian techniques were used to obtain the exact phase diagram ͑with no approximations͒, and that corresponding to the regular approximation. Remarkable agreement for some properties, such as the solvus critical point, the congruential melting, the melting points of the pure elements, and the formation entropy of the alloy, contrasts with the poor prediction of the location of the solidus-liquidus lines, reflecting errors in the heat of solution in the liquid phase. The results are compared with recent experimental reassessment of the Au-Ni phase diagram and with ab initio calculations.

The existence of the x-ray magneto-optical Voigt effect is demonstrated. By means of polarization analysis the Voigt rotation and ellipticity of linearly polarized synchrotron radiation are measured at the Co L 3 edge upon transmission through an amorphous Co film. The observed x-ray Voigt rotation is about 7.5 ± ͞mm. On the basis of ab initio calculations it is shown that the x-ray Voigt effect follows sensitively the amount of spin polarization of the 2p core states. Therefore it provides a unique measure of the spin splitting of the core states.

We present experimental magneto-optical (MO) Faraday rotation data obtained with linearly polarised soft X-ray synchrotron radiation at the 2p-3d resonance in Fe films. The dichroism of the dispersive and absorptive parts of the refraction index are compared with ab initio calculations based on the local approximation to spin-density functional theory.

We propose that carbon schwarzites-triply-periodic sp 2 networks with negative Gaussian curvature-are candidate high-temperature superconductors accessible via conventional electron-phonon coupling. Using a single-orbital tight-binding model for the D-type C 168 schwarzite (space group Im 3m, 168 atoms per unit cell), we show that the heptagonal rings intrinsic to the minimalsurface geometry induce anomalously flat bands (bandwidth < 0.3 eV) at the H and N points of the cubic Brillouin zone, producing sharp van Hove singularities in the density of states with N (E F ) ≈ 8.4 eV -1 per unit cell at optimal electron doping δ ≈ 0.15 e/atom-roughly three times the graphene value at comparable doping. Applying the Hopfield-McMillan framework with the schwarzite phonon spectrum (ω log = 1150 K), we obtain an electron-phonon coupling constant λ ≈ 0.82 and a McMillan-Allen-Dynes critical temperature T c = 46-57 K, placing hypothetical doped C 168 above all known phonon-mediated carbon superconductors without recourse to exotic chemistry, magnetic fluctuations, or van der Waals heterostructures. This geometry-driven mechanism-absent from the superconductivity literature on carbon allotropes-constitutes a new design principle: curvature as a tuning parameter for electron-phonon enhancement.

We report the first ab initio density functional theory (DFT) calculations of the electronic structure of a D-type carbon schwarzite with Im-3m symmetry, using a 136-atom unit cell (C136). Using the Quantum ESPRESSO package with PBE exchange-correlation functional, PAW pseudopotentials, and Marzari-Vanderbilt cold smearing, we performed variable-cell relaxation followed by self-consistent field calculations on the optimized geometry (a = 14.911 Å). The electronic structure reveals a robustly metallic ground state with density of states at the Fermi level N (EF ) = 34.24 states/eV/cell -a factor of 12× larger than the tight-binding estimate at charge neutrality for the related C168 model (a different parametrization of the same D-type TPMS) [1], and 4× larger than the tight-binding value at optimal electron doping. A prominent van Hove singularity peak appears at E -EF ≈ +0.95 eV (DOS = 61 states/eV/cell), arising from the saddle-point topology of the negatively curved carbon surface. Projected DOS analysis reveals σ-orbital dominance at EF (p ⊥ /p ∥ = 0.52), confirming curvature-induced π/σ hybridization. Direct application of Hopfield scaling yields λ ∼ 3.3, formally corresponding to Tc ∼ 200 K within the Allen-Dynes formulathough beyond its reliable regime (λ < 2), requiring full Eliashberg calculations. The electronic prerequisite for strong phonon-mediated superconductivity is unambiguously met. Density functional perturbation theory phonon calculations are identified as the essential next step.

Hydration of the adenine and thymine cations was studied in the gas phase. Metastable fragmentation of the cluster ions was used to draw information on the relative strengths of the binding energy of each additional solvent molecule. Both cations of adenine and thymine exhibited a well-defined hydration shell structure, with the first hydration shell complete with four water molecules. On the other hand, the hydration shell structure for the cation dimer of adenine was less evident, but appeared to require seven or eight water molecules for the first hydration shell. An ab initio calculation was carried out at the Hartree-Fock level to address some of these issues. (Int J Mass Spectrom 219 (2002) 11-21)

L'architecture de ce système ne repose pas sur une construction artificielle, mais sur une extraction. Comme dans l'archéologie, nous isolons le Grain de Cristal des Ruines pour en révéler la structure originelle. C'est le passage de la grisaille du choc à la clarté de la radiation.

Quantum Information Theory is a new field with potential implications for the conceptual foundations of Quantum Mechanics through density matrices. In particular, information entropies in Hilbert space representation are highly advantageous in contrast with the ones in phase space representation since they can be easily calculated for large systems. In this work, novel von Neumann conditional, mutual, and joint entropies are employed to analyze the dissociation process of small molecules, Cl 2 and HCl, by using the spectral decomposition of the first reduced density matrix in natural atomic orbital-based representation which allows us to assure rotational invariance, N-and v-representability in the Atoms-in-Molecules (AIM) scheme. Quantum information entropies permit to analyze the dissociation process through quantum mechanics concepts such as electron correlation and entanglement, showing interesting critical points which are not present in the energy profile, such as charge depletion and accumulation, along with bond breaking regions.

Quantum Information Theory is a new field with potential implications for the conceptual foundations of Quantum Mechanics through density matrices. In particular, information entropies in Hilbert space representation are highly advantageous in contrast with the ones in phase space representation since they can be easily calculated for large systems. In this work, novel von Neumann conditional, mutual, and joint entropies are employed to analyze the dissociation process of small molecules, Cl 2 and HCl, by using the spectral decomposition of the first reduced density matrix in natural atomic orbital-based representation which allows us to assure rotational invariance, N-and v-representability in the Atoms-in-Molecules (AIM) scheme. Quantum information entropies permit to analyze the dissociation process through quantum mechanics concepts such as electron correlation and entanglement, showing interesting critical points which are not present in the energy profile, such as charge depletion and accumulation, along with bond breaking regions.

Information Theory (IT) in conjugated and in Hilbert spaces is employed to analyze the growing behavior of nanostructures. Shannon entropies in position and momentum spaces require costly and time-consuming computations as the size of the molecules increases in contrast with information entropies in Hilbert space, which are shown to be highly advantageous for analyzing large molecules. In this work, ab initio electronic structure calculations at the HF, MP2 and B3LYP levels of theory were performed to analyse the initial steps towards growing nanostructured molecules of Polyamidoamine (PAMAM) dendrimers, starting from the monomers, dimers, trimers, tetramers up to generations G0 (with 84 atoms), G1 (228 atoms), G2 (516 atoms), and G3 (1092 atoms). This is achieved by using selected physical descriptors such as the radius of gyration, the asphericity factor, the moments of inertia, the dipole moments, the total energies and chemical reactivity indices such as the hardness, softness and the electrophilicity index at the HF/3-21G* level of theory. For the chemical indices, higher level calculations at the B3LYP/6-311++G** and MP2/6-311+G* levels were also performed in order to account for the effects of electron correlation. Information-theoretic measures of the Shannon type in conjugated space are employed to characterize the G0-PAMAM precursors and G0. Hilbert space entropies of the Shannon and Kullback type are employed to provide theoretic-information evidence of the validity of the densecore model of PAMAM precursors and dendrimers G0 through G3.

In this work, we investigate quantum entanglement-related aspects of the dissociation process of some selected, representative homo-and heteronuclear diatomic molecules. This study is based upon high-quality ab initio calculations of the (correlated) molecular wavefunctions involved in the dissociation processes. The values of the electronic entanglement characterizing the system in the limit cases corresponding to (i) the united-atom representation and (ii) the asymptotic region when atoms dissociate are discussed in detail. It is also shown that the behaviour of the electronic entanglement as a function of the reaction coordinate R exhibits remarkable correspondences with the phenomenological description of the physically meaningful regimes comprising the processes under study. In particular, the extrema of the total energies and the electronic entanglement are shown to be associated with the main physical changes experienced by the molecular spatial electronic density, such as charge depletion and accumulation or bond cleavage regions. These structural changes are characterized by several selected descriptors of the density, such as the Laplacian of the electronic molecular distributions (LAP), the molecular electrostatic potential (MEP) and the atomic electric potentials fitted to the MEP.

Quantum ab initio calculations and quantum semiempirical molecular-dynamics simulations were employed to study reconstructions of ͑100͒ diamond surfaces in the presence of hydrogen and oxygen. The results indicate that the energetically most favorable structures of oxygenated surfaces are those with chemisorbed hydroxyl groups. It was found that hydrogen bonds are formed among chemisorbed oxygenated species. The formation of these hydrogen bonds lowers the adlayer energy. A number of important vibrational modes characteristic of oxygenated diamond surfaces were identified. The analysis of surface vibrational spectra demonstrates the influence of the local environment on the position of vibrational modes and can be useful for interpretation of experimental data. ͓S0163-1829͑97͒09504-0͔

We present an experimental investigation of the UV photochemistry of diacetylene under collisionless conditions. The H loss channel is studied using DC slice ion imaging with two-color reduced-Doppler detection at 243 nm and 212 nm. The photochemistry is further studied deep in the vacuum UV, that is, at Lyman-alpha (121.6 nm). Translational energy distributions for the H + C 4 H product arising from dissociation of C 4 H 2 after excitation at 243, 212, and 121.6 nm show an isotropic angular distribution and characteristic translational energy profile suggesting statistical dissociation from the ground state or possibly from a low-lying triplet state. From these distributions, a two-photon dissociation process is inferred at 243 nm and 212 nm, whereas at 121.6 nm, a one-photon dissociation process prevails. The results are interpreted with the aid of ab initio calculations on the reaction pathways and statistical calculations of the dissociation rates and product branching. In a sec...

The results of most B3LYP and B3PW simulations, performed during the last quarter of century, dealing with ABO perovskite (001) surfaces, heterostructures, and oxygen vacancies therein, were reviewed. According to carried out B3LYP and B3PW simulations, almost all upper-layer atoms on the BO 2-and AO-terminated STO, BTO, PTO, CTO, SZO, BZO, PZO, and CZO perovskite (001) surfaces shift inwards. Practically all ABO perovskite second-layer atoms shift upwards. Finally, nearly all third-layer atoms, once more, shift inwards. The ABO perovskite (001) surface energies, for both BO 2 and AO terminations, are comparable. Computer simulations on the ABO perovskites indicate a significant rise of the B-O chemical bond covalency nearby the BO 2-terminated (001) surfaces in comparison to their bulk. B3LYP-and B3PW-simulated ABO perovskite bulk Γ-Γ band gaps are decreased nearby their BO 2-and AO-terminated (001) surfaces. We discuss recent B3PW simulations for the STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures. Simulated optical band gaps of the STO/BTO, STO/PTO, and SZO/PZO (001) heterostructures mainly depend on the BO 2-or AO-terminations of the upper layer of the augmented film. The displacement magnitudes of the nearest neighbor atoms, around the (001) surface oxygen vacancy, in the ABO perovskites, usually, are larger than in their bulk. In the STO, BTO, PTO, and SZO perovskites, the electronic charge, ordinarily, is a lot better localized inside the bulk than the (001) surface oxygen vacancy. In the STO, BTO, PTO, and SZO perovskites, the (001) surface oxygen vacancy-induced defect levels are located closer to the conduction band bottom than in the bulk cases. Simulated formation energy difference between the bulk and the (001) surface oxygen vacancies in the STO, BTO, PTO, and SZO perovskites triggers the oxygen vacancy segregation from the bulk towards the (001) surface. All computer simulations for ABO perovskites were performed in their high-symmetry cubic phase.

The Raman spectra of protonated and deuteriated powder samples of α-D-glucose, 2-deoxy-D-glucose, 2-fluoro-2-deoxy-D-glucose, 3-fluoro-3-deoxy-D-glucose and 6-fluoro-6- deoxy-D-glucose have been examined. In addition ab initio calculations of the molecular structures of the aforementioned molecules and their associated vibrational modes have been conducted using the hybrid SCF-DFT (B3-LYP) method incorporating a cc-pVDZ basis set.

The theoretical methods currently in use for the calculation of surface phonon dispersion curves and how they have evolved from the phenomenological force-constant models to the present day first principles theories are discussed. A selection of paradigmatic examples for the different classes of crystal surfaces is presented with comparisons to the experimental data obtained from helium atom scattering or electron energy-loss spectroscopy.

We present the results of a comparative study of the equilibrium crystal structure and vibrational properties of the Na∕Cu(111) system at coverages up to monolayer saturation. The calculations are performed with interaction potentials from the embedded-atom method. The following ordered structures are considered: p(3×3), p(2×2), (√3×√3)30°, nd (3∕2×3∕2). The surface relaxation, phonon dispersion, and polarization of vibrational modes for the adsorbate and substrate atoms as well as the local density of states are discussed. It is found that the bond length between an adsorbate and the nearest-neighbor substrate atom slightly increases with increasing coverage. Adsorption of sodium also results in a small rumpling in two upper substrate layers. The mode associated with adatom-substrate stretch vibrations was obtained in our calculation at about 22meV for all the structures considered. The strength of this mode decreases with increasing coverage in accordance with the experiment. On t...

The bond charge model (BCM), originally designed by Weber for the dynamics of tetrahedrally coordinated semiconductors, is shown to be applicable, with minor adjustments, to sp2 configurations. Calculations for the bulk and surface dynamics of graphite, based on a comparatively small number of adjustable parameters (five or six), are shown to be in excellent agreement with recent inelastic helium atom scattering data and high-resolution electron-energy-loss spectroscopy. The parameter transferability to other forms of sp2-bonded carbons is discussed with the indication that BCM is easily applicable to large structures (e.g., giant fullerenes) presently inaccessible to ab initio methods, with a comparatively modest computational effort

Experimental evidence of two-phonon vibronic progressions due to second-order linear electron-phonon interactions is obtained in NiCl, and NiBr, crystals, by comparing the phonon structure observed in 'A2{F)~'E{D) transition With Raman data. The vanishing of the spin-dependent first-order electron- phonon interaction is shown to be a necessary condition for observing prominent second-order phonon structures in isoconfigurational crystal-field transitions. According to this rule we predict and discuss. the appearance of second-order progressions in other d-metal layered compounds.

By studying a series of adatoms on representative transition-metal surfaces through first-principles calculations, we establish a clear correlation between the preferred mechanism and activation energy for adatom descent at a step and the relative degree of electronic shell filling of the adatom and the substrate. We also find an approximate linear relation between the adatom step-edge hopping barriers and the adatom-surface bonding strength with slope roughly proportional to the number of the adatom's nearest neighbors initially. These results may serve as simple guiding rules for predicting precise atomic surface morphologies in heteroepitaxial growth, as in formation of nanowires.

By studying a series of adatoms on representative transition-metal surfaces through first-principles calculations, we establish a clear correlation between the preferred mechanism and activation energy for adatom descent at a step and the relative degree of electronic shell filling of the adatom and the substrate. We also find an approximate linear relation between the adatom step-edge hopping barriers and the adatom-surface bonding strength with slope roughly proportional to the number of the adatom&#39;s nearest neighbors initially. These results may serve as simple guiding rules for predicting precise atomic surface morphologies in heteroepitaxial growth, as in formation of nanowires.

This ms was written using ''century schoolbook'' and, whenever necessary, ''symbol'' fonts. A careful distinction was made between italic vee's and Greek nu's both in the text and in formulas, that is important to respect. It will only be visible if using ''century schoolbook'' as the major font to visualize and print the text.

We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H 2 O-Ar in the 2OH excitation range of H 2 O. 24 sub-bands have been observed. Their rotational structure (T rot = 12 K) is analyzed and the lines are fitted separately for ortho and para species together with microwave and far infrared data from the literature, with a unitless standard deviation σ = 0.98 and 1.31, respectively. Their vibrational analysis is supported by a theoretical input based on an intramolecular potential energy surface obtained through ab initio calculations and computation of the rotational energy of sub-states of the complex with the water monomer in excited vibrational states up to the first hexad. For the ground and (010) vibrational states, the theoretical results agree well with experimental energies and rotational constants in the literature. For the excited vibrational states of the first hexad, they guided the assignment of the observed sub-bands. The upper state vibrational predissociation lifetime is estimated to be 3 ns from observed spectral linewidths.

Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong uniaxial magnetic anisotropy above its ∼90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) measurements at the Mn K and Bi L 2,3 edges show induced magnetism in Bi, which is strongly coupled to the magnetism of Mn. Temperature-and pressure-dependent XMCD results reveal that hydrostatic pressure mimics the effect of temperature, driving a transition from uniaxial to in-plane anisotropy. The pressure and temperature transitions are shown to be connected to an anisotropic lattice contraction in NiAs-type structures. Temperature and pressure, hence, induce coupled structural and magnetic responses, highlighting the importance of both anisotropic lattice change and Mn-Bi hybridization in leading to the magnetic anisotropy change across the SRT. The dependence of magnetic anisotropy on the anisotropic lattice change is confirmed by density functional theory.

Assessment of the glaucophane substitution, [M4] Ca + [VI] Mg ´ [M4] Na + [VI] Al, along the Ga and F analogue of the tremolite-glaucophane join, ■ ■Ca 2 Mg 5 Si 8 O 22 F 2 -■ ■Na 2 Mg 3 Ga 2 Si 8 O 22 F 2 (= F-Ga-glauc), was conducted at 900 ∞C and 1.5 GPa in 10 mol% increments. Several chemical exchanges deviating from the glaucophane substitution were identified, namely the "edenite" substitution [A] ■ ■ + [IV] Si [A] Na + [IV] Ga toward F-Ga-nyböite, the [A] ■ ■ + [M4] Na + [VI] Ga + [IV] Si ´ [A] Na + [M4] Mg + [VI] Mg + [IV] Ga exchange toward F-Ga-Na-magnesiokatophorite, and the [A] ■ ■ + [VI] Ga ´ [A] Na + [VI] Mg exchange toward F-Ga-eckermannite. Minor displacements from the join due to the [M4] Na + [VI] Ga [M4] Mg + [VI] Mg exchange toward "cummingtonite" and the richterite exchange [A] ■ ■ + [M4] Ca ´ [A] Na + [M4] Na were also observed. Amphibole syntheses with low F-Ga-glauc contents (£60 mol%) were primarily influenced by the "edenite" exchange, while those with high F-Ga-glauc contents (ª70 mol%) were dominated by the "glaucophane" substitution. Powder X-ray diffraction Rietveld refinements were obtained without restrictions for the amphiboles formed in the range 0-40 mol% F-Ga-glauc. Refinements for samples in the ranges of 50-70 and 100 mol% F-Ga-glauc were possible only after applying some restrictions to the A-and M4-site occupancies because of the appearance of a layered silicate and an unidentified Ga-rich phase that complicated the refinement. The successful refinements indicated that amphibole exhibits [VI] Ga ordering at the M2 site and [IV] Ga ordering at T1. The refinements also show a transition in A-site occupancy from A2 to Am with increasing F-Ga-glauc content. The inability to synthesize stoichiometric glaucophane and the types of chemical deviations that are observed in this analogue system are virtually identical to what has been observed in previous studies. Extrapolation of the results from this and previous studies suggests that ideal glaucophane would be obtained at approximately 3.85 GPa and 585 ∞C.

metamorphic facies to forming the basis of geothermobarometry, if their thermodynamic mixing properties can be calibrated to the temperature and pressure of formation. Compositional variations of sodium-and sodium-calcium-amphiboles may reveal important information about paleo-subduction zones but have not been studied as much as the more common calcium-amphiboles. In this study we investigate the mixing properties of amphibole solid solutions between magnesio-hornblende and glaucophane [ B Ca 2 C (Mg 4 Al) T (AlSi 7 )O 22 (OH) 2 -B Na 2 C (Mg 3 Al 2 ) T (Si 8 )O 22 (OH) 2 ] as a binary sub-join within the ternary amphibole system tremolite-glaucophane-tschermakite where the principal substitutions are Ca for Na at the B, Al for Mg at the C, and Al for Si at the T crystallographic sites. Amphiboles were made from mixtures of reagent oxides at 10 mol% increments between magnesio-hornblende and glaucophane, formed in a piston-cylinder press at 735-860 C and 1.3-2.5 GPa for 72-216 h giving good yields (92-100 wt%). A positive deviation is present in the volume-composition plot, even after correcting volumes for non-binary components, supporting the presence of a positive deviation in the enthalpy of mixing ( H mix ) along this join. Fourier transform infrared spectra (FTIR) were obtained in the range of 350-4000 cm -1 for the mid-infrared spectra (MIR) for the purpose of estimating the extent of short-range ordering and for autocorrelation analysis, and, in the 650-50 cm -1 , for far-infrared spectra (FIR) for autocorrelation analysis. Autocorrelation analysis gave Corr values, which further support a positive deviation in the H mix along the magnsio-hornblende-glaucophane join, although the Corr maximum did not occur at the calcium-poor (i.e., glaucophane-rich) portion of the join as expected. Synthetic end-member glaucophane and magnesio-hornblende were mixed in a molar ratio of 1:1 and allowed to equilibrate by homogenization for variable durations in the range of 600-800 C at 2.0 GPa to determine the maximum-width of the miscibility gap. These compositional re-equilibration experiments suggested the presence of an asymmetric miscibility gap (steeper toward glaucophane) with a critical-point below 700 C. Combining the results of this study with previously ism mixing parameters (i.e., W Gl,Ts = 20 kJ, Ts = 1.2) and modeling of the miscibility gap within the tremolite-glaucophane-tschermakite ternary system. The results showed that the composition of the critical point is very close to the maximum in the autocorrelation parameter Corr, as one would predict. An important implication of this study is that low-temperature immiscibility between calciumand sodium-rich amphiboles may be more important than the role of pressure, as proposed by Brown (1977), in accounting for the change in B-site Na contents of metamorphic amphiboles.

Reactivity of various R–CO–X carbonyl compounds toward hydrogenation was compared on Re–Pt/Al2O3 catalyst containing 1wt.% of both metals. In the R–CO–X carbonyl compounds the R is aliphatic, saturated and unsaturated group up to 16 carbon atoms or phenyl, while the group X refers to H, R′, OR′, OH, NH2, NR′ and NR′R″ i.e. aldehyde, ketone, ester, carboxylic acid, primary, secondary

This study investigates the physical properties of the double perovskite oxide series A 2 TiCrO 6 (A = Mg, Ca, Sr, Ba, Ra) using different exchange-correlation functionals based on density functional theory (DFT). Structural stability of the A 2 TiCrO 6 compounds at the equilibrium lattice constant ensures the cubic Fm 3 m symmetry through analyses of tolerance factors, while the Birch-Murnaghan equation reveals that the ferromagnetic (FM) phase is energetically preferred over the non-magnetic (NM) configuration. The spin-polarized electronic band structure and density of states (DOS) demonstrated that all compounds under investigation are half-metallic with nearly integral magnetic moments of 2 𝜇 B. The PDOS analysis indicates that the valence band is dominated by O-2p orbitals, while Ti-d states prevail in the conduction band near the Fermi level. All the compounds satisfy Born stability criteria and the ductile nature of the materials was demonstrated through Poisson's, Pugh's ratios, and Cauchy's pressure. The dynamical stability of these compounds is demonstrated through phonon dispersion curves. In thermodynamic properties, the high melting temperature and specific heat capacities demonstrate that the investigated compounds are thermally suitable for high-temperature device applications. Optical analyses show that the static refractive index exceeds unity and aligns well with predictions from the Penn model. Furthermore, the absorption, refractive index, extinction coefficient, and optical conductivity spectra suggest that these compounds are suitable for UV-based optoelectronic applications. The electronic, optical, mechanical, and magnetic properties suggest that these materials are promising candidates for spintronic applications. Moreover, the coexistence of high spin polarization, a tunable dielectric response, and strong UV optical activity establishes the A 2 TiCr O 6 compounds as multifunctional materials suitable for spintronic and optoelectronic applications.

The adiabatic ionization potential of the BaOH radical, as generated in a laser vaporizationsupersonic expansion source has been determined by laser photoionization experiments to be (4.55 ± 0.03) eV. This value supports the three lowest out of seven previous experimental estimates, the former ranging from 4.35 to 4.62 eV. The present result is compared to ab initio calculations, as performed using both quantum chemistry at different levels of theory and density functional theory, and trying several effective core potentials and their accompanying basis sets for Ba. The most satisfactory agreement is obtained for either the adiabatic or vertical ionization potentials that derive from post-Hartree-Fock [MP2 and CCSD(T)] treatments of electron correlation, along with consideration of relativistic effects and extensive basis sets for Ba, in both BaOH and BaOH + . Such conclusions extend to the results of related calculations on the Ba-OH dissociation energies of BaOH and BaOH + , which were performed to help in calibrating the present computational study. Bonding in BaOH/BaOH + , as well as possible sources of discrepancy with previous experimental determinations of the BaOH adiabatic ionization potential are discussed.

The adiabatic ionization potential of the BaOH radical, as generated in a laser vaporization-supersonic expansion source has been determined by laser photoionization experiments to be (4.55 ± 0.03) eV. This value supports the three lowest out of seven previous experimental estimates, the former ranging from 4.35 to 4.62 eV. The present result is compared to ab initio calculations, as performed using both quantum chemistry at different levels of theory and density functional theory, and trying several effective core potentials and their accompanying basis sets for Ba. The most satisfactory agreement is obtained for either the adiabatic or vertical ionization potentials that derive from post-Hartree-Fock [MP2 and CCSD(T)] treatments of electron correlation, along with consideration of relativistic effects and extensive basis sets for Ba, in both BaOH and BaOH(+). Such conclusions extend to the results of related calculations on the Ba-OH dissociation energies of BaOH and BaOH(+), whic...

The adiabatic ionization potential of the BaOH radical, as generated in a laser vaporizationsupersonic expansion source has been determined by laser photoionization experiments to be (4.55 ± 0.03) eV. This value supports the three lowest out of seven previous experimental estimates, the former ranging from 4.35 to 4.62 eV. The present result is compared to ab initio calculations, as performed using both quantum chemistry at different levels of theory and density functional theory, and trying several effective core potentials and their accompanying basis sets for Ba. The most satisfactory agreement is obtained for either the adiabatic or vertical ionization potentials that derive from post-Hartree-Fock [MP2 and CCSD(T)] treatments of electron correlation, along with consideration of relativistic effects and extensive basis sets for Ba, in both BaOH and BaOH + . Such conclusions extend to the results of related calculations on the Ba-OH dissociation energies of BaOH and BaOH + , which were performed to help in calibrating the present computational study. Bonding in BaOH/BaOH + , as well as possible sources of discrepancy with previous experimental determinations of the BaOH adiabatic ionization potential are discussed.

The ab initio No-Core Shell Model (NCSM) begins with an intrinsic Hamiltonian for all nucleons in the nucleus. Realistic two-nucleon and tri-nucleon interactions are incorporated such as those recently developed from effective field theory and chiral perturbation theory. We then derive a finite basis-space dependent Hermitian effective Hamiltonian that conserves all the symmetries of the initial Hamiltonian. The resulting finite Hamiltonian matrix problem is solved by diagonalization on parallel computers. Applications range from light nuclei to multiquark systems and, recently, to quantum field theory including systems with bosons. We present this approach with a sample of recent results.

We examine the importance of conserving the vector current in calculating low-energy neutrino-nucleus interactions by implicitly invoking Siegert&#39;s Theorem in describing the vector transverse electric current. We find that at low neutrino energies (E? &lt;50 MeV), Siegert&#39;s Theorem can change neutrino cross sections for normal-parity non-spin-flip excitations by about a factor of two.The same is true of muon capture rates. At higher neutrino energies the effect of Siegert&#39;s Theorem diminishes, and by about 100 MeV the effect is very small.