Ab Initio

I nterest in the chemistry of the early actinide elements (notably uranium through americium) usually results either from the nuclear waste problem or the unique chemistry of these elements that result from 5f contributions to bonding. Computational actinide chemistry provides one useful tool for studying these processes.

First-principles virtual tensile and shear test calculations have been performed to Al(0 03)//-AlFeSi(0 0 1) and Al(01 4)//Fe 4 Al 13 (1 01) interfaces by the ab initio pseudo potential density functional theory method. Work of separation, ultimate tensile strength and shear strength of bulk and interface structures were calculated. The Al (0 03)/-AlFeSi(0 0 1) interface showed higher tensile strength than the Al(01 4)//Fe 4 Al 13 (1 01) interface structure. Moreover, interface calculations revealed a charge depletion region in the second layer of the Fe 4 Al 13 structure, which caused lower work of separation. Furthermore, shear calculations showed stronger shear strength for the Al(01 4)//Fe 4 Al 13 (1 01) interface than for the Al(0 0 1)//-AlFeSi(0 0 1) interface structure.

Analisis del problema historico de la colonizacion griega de epoca arcaica en Occidente desde el punto de vista de cinco tendencias historiograficas actuales: Positivismo, Marxismo, Estructuralismo, Posmoder-nismo y Poscolonialismo. Comentario de los diferentes metodos interpretativos que emplea cada una de ellas en relacion con el objeto de estudio en cuestion.

By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem DFT has recently emerged as a powerful tool for reducing the computational scaling of Kohn-Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extening FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dual approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement (but still within chemical accuracy) with Kohn-Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed.

"En este trabajo realizamos cálculos de primeros principios para investigar las propiedades estructurales y electrónicas de la multicapa 1x1 CrN/GaN. Los cálculos se realizan en las fases zincblenda y wurtzita, debido a que este es el estado base del nitruro de cromo CrN y el nitruro de galio GaN, respectivamente. Sin embargo, se estudia la estabilidad de la multicapa en la fase NaCl, con el fin predecir posibles transiciones de fase. Encontramos que la fase más favorable para multicapa, es la hexagonal tipo wurtzita, con posibilidad de pasar a la fase NaCl mediante la aplicación de una presión externa. Nuestros cálculos nos permiten predecir que la presión de transición es 13,5 GPa. A partir de la densidad de estados encontramos que la multicapa posee un comportamiento metálico debido a la hibridación de los orbitales Cr-d y N-p que atraviesan el nivel de Fermi"

Chloromethyl methyl dichlorosilane (ClCH2CH3SiCl2) was synthesized and the infrared spectra of its vapour, and of the amorphous and crystalline states, cooled to the temperature of liquid nitrogen were recorded. Additional mid IR spectra of the compound, isolated in both argon and nitrogen matrices, were taken at 5K. Raman spectra of the liquid were recorded in a capillary at various temperatures

A disorder-order transition from amorphous carbon (aC) to layered amorphous graphene (LAG) has been predicted using ab-initio methods. Amorphous carbon at densities close to the graphitic density show a strong proclivity to layer in NVT simulations near 3000K . Our calculations have shown that graphitization is strongly dependent on the simulation temperature and is not observed under 2500K. The origin of such a disorderorder transition has been studied using various structural analyses. Each layer of LAG is a layer of amorphous graphene (aG) including pentagons and heptagons in addition to hexagons and the planes are separated by about 3.2Å. LAG obtained from the NVT simulations were highly stable. The electronic charge density, especially for the π and π∗ states, was computed with the Hyed-Scuseria-Ernzerhof (HSE) hybrid functional and compared with crystalline graphite (cG). The impact of structural disorder has been studied in detail, especially the consequences of disorder to e...

Density functional theory (DFT) and thermal DFT (thDFT) calculations were used to evaluate the energy band structure, bandgap, and the total energy of various graphene quantum dots (GQDs). The DFT calculations were performed using local density approximation for the exchange-correlation functional and norm-conserving pseudopotentials. We consider the triangular and hexagonal GQDs with zigzag and armchair edges and 1-3 nm dimensions with many hundred atoms. The simulation results show that all of these GQDs are direct bandgap semiconductors with a flat band structure, and they are suitable for electronics and optoelectronics applications. Analysis of GQDs in which the A and B sublattice symmetries were broken showed degenerate zero-energy shells. Using the thDFT calculations carried out at temperatures up to 1400 K, we evaluated the temperature dependence of the GQDs bandgaps and total energies via entropy-term and electron’s kinetic energy. The obtained results indicate that the gro...

Several years ago we embarked on a project to calculate optimal crystal-packing and crystalstructure parameters based on potential functions from energy-partitioned ab-initio intermolecular SCF calculations plus calculations of dispersion energy contributions. Our approach, aimed at evaluating the intermolecular interactions, such as in polymer propagation and in molecular crystals, and at analyzing the optimal crystal packing, is based on nonempirical ab-inirio calculations for smaller molecular aggregates (monomers, dimers, trimers, etc.), partitioning the total SCF interaction energies into the .different components, and then fitting these components individually to functional forms or when necessary recalculating or estimating explicitly for certain interaction components for each different unit cell dimension change. We derived and implemented a complete program, including higher order terms and special features necessary only for calculations on crystals. We also derived and implemented a complete CRYSTAL program which, given the crystal symmetry, allows us to vary and optimize the crystal-structure parameters. We carried out test crystal optimization calculations on N2 and on C02 both to check out the entire CRYSTAL program package and to explore the extensive programs written for various ab-initio based methods for calculating reliable intermolecular interactions. We investigated such aspects as the comparison of the various intermolecular interaction terms calculated from the potential functions compared with those calculated by ob-initio wave functions. We also investigated for the CRYSTAL program how many surrounding unit cells had to be included for energy convergence. We investigated the crystal CH~NOZ. We calculated the intermolecular interactions at more than 50 geometries, partitioned the interaction energies, and fit these to functional forms. The agreement of our calculated unit cell dimensions with experiment was excellent, within I to 2.8%. Furthermore, our method fits the partitioned ~E X F results to atom-class-atom-class potential functions, which enables a general library of such potential functions to be built up for the molecular classes of interest.

Structure D 2000 Ab initio Structure Determination of Novel Borate NaSrBO 3 .-The novel title compound is successfully synthesized by solid state reaction of Na2CO3, SrCO3, and H3BO3 (650→850°C, 72 h) and its structure is refined from powder XRD data. NaSrBO3 crystallizes in the monoclinic space group P21/c with Z = 4. The fundamental building units are isolated BO3 groups, which are parallelly distributed along two different directions. Because of the anisotropic polarizations of planar BO 3 groups, a considerable birefringence can be expected. NaO6 octahedra and SrO9 tri-capped trigonal prisms are connected via common O atoms to form an infinite three-dimensional network.

Spectral comparison is an important part of the assignment of the absolute configuration (AC) by vibrational circular dichroism (VCD), or equally by Raman Optical Activity (ROA). In order to avoid bias caused by personal interpretation, numerical methods have been developed to compare measured and calculated spectra. Using a neighbourhood similarity measure, the agreement between a computed and measured VCD or ROA spectrum is expressed numerically to introduce a novel confidence level measure. This allows users of Vibrational Optical Activity (VOA) techniques (VCD and ROA) to assess the reliability of their assignment of the AC of a compound. To that end, a database of successful AC determinations is compiled along with neighbourhood similarity values between the experimental spectrum and computed spectra for both enantiomers. For any new AC determination, the neighbourhood similarities between the experimental spectrum and the computed spectra for both enantiomers are projected on the database allowing an interpretation of the reliability of their assignment.

Brandejs J., Višňák J., Veis L., Maté M., Legeza Ö., Pittner J.: Toward DMRG-tailored coupled cluster method in the 4c-relativistic domain

There are three essential problems in computational relativistic chemistry: Electrons moving at relativistic speeds, close lying states, and dynamical correlation. Currently available quantum-chemical methods are capable of solving systems with one or two of these issues. However, there is a significant class of molecules in which all the three effects are present. These are the heavier transition metal compounds, lanthanides, and actinides with open d or f shells. For such systems, sufficiently accurate numerical methods are not available, which hinders the application of theoretical chemistry in this field. In this paper, we combine two numerical methods in order to address this challenging class of molecules. These are the relativistic versions of coupled cluster methods and the density matrix renormalization group (DMRG) method. To the best of our knowledge, this is the first relativistic implementation of the coupled cluster method externally corrected by DMRG. The method brings a significant reduction of computational costs as we demonstrate on the system of TlH, AsH, and SbH.

For arxiv version, see:  https://arxiv.org/pdf/2001.05352.pdf

The structural, electronic and optical properties of sodium nitrate are investigated using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA). The geometrical parameters of the unit cell have been fully optimized and are in good agreement with the experimental data. The electronic structure shows that sodium nitrate has a band gap of 2.917 eV. The dielectric functions, reflective index, extinction coefficient, reflectivity and energy-loss spectrum are calculated. The optical properties of sodium nitrate are discussed based on the band structure calculations. The 2p states of the nitrate moiety play the major role in optical transitions as initial and final states. The absorption spectrum is localized in the ultraviolet range between 60 and 380 nm.

Recently, we proposed a hierarchical model for the elastic properties of mineralized lobster cuticle using (i) ab initio calculations for the chitin properties and (ii) hierarchical
homogenization performed in a bottom-up order through all length scales. It has been found that the cuticle possesses nearly extremal, excellent mechanical properties in terms of stiffness that strongly depend on the overall mineral content and the specific microstructure of the mineral–protein matrix. In this study, we investigated how the overall cuticle properties changed when there are significant variations in the properties of the constituents (chitin, amorphous calcium carbonate (ACC), proteins), and the volume fractions of key structural elements such as chitin–protein fibers. It was found that the cuticle performance is very robust with respect to variations in the elastic properties of chitin and fiber proteins at a lower hierarchy level. At higher structural levels, variations of design parameters such as the volume fraction of the chitin–protein fibers have a significant influence on the cuticle performance. Furthermore, we observed that among the possible variations in the cuticle ingredients and volume fractions, the experimental data reflect an optimal use of the structural variations regarding the best possible performance for a given composition due to the smart hierarchical organization of the cuticle design.

In this work, a combined experimental and theoretical study on molecular structure, vibrational spectra of 1-amino-2,6-dimethylpiperidine (ADP) has been reported. The FTIR and FT-Raman spectrum have been recorded in the region 4000-400 cm -1 and 3500-50 cm -1 , respectively. The molecular geometry, harmonic vibrational frequencies and bonding features of ADP have been calculated by using ab initio /HF and density functional theory/B3LYP methods with 6-31+G(d,p) basis set. A detailed interpretation of the FTIR, FT-Raman, NMR spectra of ADP has also been reported. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. Energy of the highest occupied molecular (HOMO) orbital and lowest unoccupied (LUMO) molecular orbital have been predicted.

The infrared spectrum (3200-400 cm À1) of the gas and the Raman spectrum (3200-50 cm À1) of liquid and solid 1,1-difluoro-1-silacyclopentane and 1,1-dichloro-1-silacyclopentane have been recorded. In all of these physical states only the twisted (C 2) conformer was detected. The conformational energies have been calculated with the Moller-Plesset perturbation method to the second order; MP2(Full) as well as the density functional theory by the B3LYP method utilizing a variety of basis sets up to 6-311 + G(2df,2pd). All the calculations predict only the twisted form as the stable conformer of 1,1difluoro-1-silacyclopentane with the average barrier to planarity of 2548 cm À1 (30.49 kJ/mol) from the MP2 calculations and a significantly lower value of 1422 cm À1 (17.01 kJ/mol) from the density functional calculations. Neither calculation was significantly affected by the inclusion of diffuse functions. The C s conformer has a lower energy of 1703 cm À1 (MP2) and 1334 cm À1 (B3LYP) than the planar form. Thus the path between the two identical C 2 conformers is by pseudorotational motion rather than through the planar form. Similar results obtain for 1,1-dichloro-1-silacyclopentane. The optimized geometry calculated with the 6-311 + G(2df,2pd) basis is given together with a complete vibrational assignment for the twisted (C 2) conformer. These assignments are supported by normal coordinate calculations with scaled force constants from MP2(Full)/6-31G(d) calculations. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for silacyclopentane.

The tunneling mechanisms of electron transfers (ETs) in photosynthetic reaction center of Blastochloris viridis are studied by the ab initio fragment molecular orbital (FMO) method combined with the generalized Mulliken-Hush (GMH) and the bridge Green function (GF) calculations of the electronic coupling T DA and the tunneling current method for the ET pathway analysis at the fragment-based resolution. For the ET from batctriopheophytin (H L) to menaquinone (MQ), a major tunneling current through Trp M250 and a minor back flow via Ala M215, Ala M216, and His M217 are quantified. For the ET from MQ to ubiquinone, the major tunneling pathway via the non-heme Fe 2+ and His L190 is identified as well as minor pathway via His M217 and small back flows involving His L230, Glu M232, and His M264. At the given molecular structure from X-ray experiment, the spin state of the Fe 2+ ion, its replacement by Zn 2+ , or its removal are found to affect the T DA value by factors within 2.2. The calculated T DA values, together with experimentally estimated values of the driving force and the reorganization energy, give the ET rates in reasonable agreement with experiments.

Abstract The ionisation process corresponding to the 2 T 2 g ← 1 A 1 g transition in Mo ( CO ) 6 is studied by employing the nuclear quantum dynamical approach and electronic structure methods. The spectrum is simulated by construction of a Hamiltonian model. The computed spectrum is found to be in a good agreement with the corresponding experimental spectrum indicating the potential energy surfaces and time-dependent population analysis are correctly computed. We investigate the contribution of the spin-orbit coupling in separation of bands of the valence ionisation spectrum corresponding to the electronic states 1 E 5 / 2 + and 1 G 3 / 2 + by carrying out a trend analysis in series transition metal complexes M ( CO ) 6 , M = Cr , Mo , W .

The ab initio cluster model approach has been applied to the study of chemisorption of atomic S on Pt(111). Hartree-Fock and explicitly correlated wave functions predict reasonable results for the equilibrium distance perpendicular to the surface and its corresponding vibrational frequency. However, the interaction energy has been shown to be largely affected by electronic correlation effects. Use of MR-MP2 and MRCI wave functions with large reference spaces results in a D e value which is surprisingly close to the experimental estimate of the interaction energy. All approaches suggest that S is strongly bonded to the Pt(111) surface through covalent interactions but also predict that chemisorbed S exhibits a rather large negative charge. Therefore, it is predicted that S chemisorption will strongly affect the electronic properties of the Pt(111) surface. This situation will be specially valid in the low-coverage limit.

We studied Structure -Activity Relationships (SAR) of a series of 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine derivatives, which present antispermatogenic activity, using Principal Component Analysis (PCA), K-Nearest Neighbor (KNN) and Neural Network (NN) methods. Firstly, we carried out thorough conformational explorations using the PM3 method, in order to determine the most stable conformations. The minima found were optimized using ab initio HF/3-21G. Molecular properties were calculated using the same ab initio method. Steric properties such as molecular volume and surface and the octanol/water partition coefficient were also calculated. A total of three variables (atomic charges on two specific atoms and the molecular volume) out of many were selected as being useful for SAR. PCA yielded a reasonable separation between high-activity and low-activity groups. The KNN and NN methods presented approximately 70% correct classifications. Finally, a set of new compounds was proposed and analyzed. q

The lowest energy electronic transitions in the weakly bound van der Waals complex of water and oxygen (H 2 O•O 2 ) are studied using ab initio methods. The vertical excitation energies for the two low-lying singlet states are calculated with the complete active space self-consistent field and multireference configuration interaction ͑MRCI͒ methods, and are compared to those calculated in the oxygen molecule. The MRCI calculations predict blueshifts of about 150 and 250 cm Ϫ1 for the transition frequencies on formation of the complex. These calculated shifts can provide assistance towards the spectroscopic identification of H 2 O•O 2 .

The electronic structure and bonding of geometrically inequivalent surface oxygens is examined for MOO3(010) and (100) surfaces where the local electronic structure is obtained from ab initio density functional theory (DFT-LCGTO) cluster calculations. The clusters are chosen as finite sections of the ideal MoO 3 surface where cluster embedding is achieved by bond saturation with hydrogens, yielding dusters up to Mo7OaoHls. Local charging, bond orders, and electrostatic potentials of the surface clusters depend weakly on cluster size, suggesting general validity for the extended surface. The difference in electronic structure between the (010) and (100) surface is found to be mainly due to the different atom arrangement, while local atom charging and binding properties are surface-independent. Terminal molybdenyl oxygens experience the smallest negative charging and form double bonds with the adjacent Mo centers. Asymmetric bridging oxygens are slightly more negative and similar in their binding scheme to molybdenyl oxygens. Symmetric bridging oxygens become most negative and form single bonds with the two neighboring Mo centers. Electrostatic potentials determined from cluster charge distributions show broad negative minima above the terminal oxygens while there are no minima above bare Mo metal centers which can affect stabilization and binding of adparticles at the MoO 3 surfaces.

Gas sensing study of C 2 H 4 Li complex toward oxides viz. CO, CO 2 , NO, NO 2 , SO, and SO 2 gas molecules has been carried out using ab initio method. Different possible configurations of gas molecule adsorption on C 2 H 4 Li complex are considered. The structural parameters of most stable configuration of gas molecule adsorbed complexes are thoroughly analysed. Electronic properties are studied using total density of states (DOS) plot. Charge transferred between the gas molecule and the substrate is studied using NBO charge analysis. Gas sensing of all the six gas molecules is possible at ambient conditions. Atom centred density matrix propagation (ADMP) molecular dynamics simulations confirmed that all the gas molecules remain adsorbed on C 2 H 4 Li complex at room temperature during the simulation. This study suggests that the C 2 H 4 Li complex acts as a novel gas sensing material for CO, CO 2 , NO, NO 2 , SO, and SO 2 gas molecules at ambient conditions, below room temperature as well as at high pressure.

DFT schemes based on conventional and less conventional exchange-correlation ͑XC͒ functionals have been employed to determine the polarizability and second hyperpolarizability of-conjugated polyacetylene chains. These functionals fail in one or more of several ways: ͑i͒ the correlation correction to ␣ is either much too small or in the wrong direction, leading to an overestimate; ͑ii͒ ␥ is significantly overestimated; ͑iii͒ the chain length dependence is excessively large, particularly for ␥ and for the more alternant system; and ͑iv͒ the bond length alternation effects on ␥ are either underestimated or qualitatively incorrect. The poor results with the asymptotically correct van Leeuwen-Baerends XC potential show that the overestimations are not related to the asymptotic behavior of the potential. These failures are described in terms of the separate effects of the exchange and the correlation parts of the XC functionals. They are related to the short-sightedness of the XC potentials which are relatively insensitive to the polarization charge induced by the external electric field at the chain ends.

The phase diagram of solid oxygen at terapascal pressures and several thousand Kelvin has been studied with ab initio density functional theory within the quasiharmonic approximation for the vibrational free energy. Our work extends previous theoretical studies done at zero temperature and shows that temperature has a dramatic effect on the sequence of phases. At low temperature, the transition from onefold (molecular) to fourfold coordination takes place through two intermediate phases with twofold coordination and space groups I 4 1 /acd and Cmcm. Above 8000 K we find that these two intermediate phases are no longer stable, and oxygen transforms directly from a molecular phase to a fourfold coordinated phase of space group F mmm. We also find that the transition between Cmcm and F mmm can be ascribed as a second-order transition driven by an electronic instability.

Unimolecular decompositions of neutral (NH 2 CHO) and protonated (NH 3 CHO +) formamide, an active precursor of biomolecules in prebiotic chemistry, are investigated in the ground (S 0) and first triplet (T 1) and singlet (S 1) excited states. Different decomposition channels including the homolytic bond dissociations, dehydration, decarbonylation, dehydrogenation, etc., are explored using coupled-cluster theory (CCSD(T)/CBS method) for both S 0 and T 1 states and RASPT2(18,15)/6-31G(d,p) computations for the S 1 state. On S 1 and T 1 energy surfaces, formamide preferentially follows C−N homolytic bond cleavages forming NH 2 + HCO radical pairs. Formation of HCN and HNC from dehydration of neutral and protonated formamide via formimic acid and aminohydroxymethylene isomers has higher energy barriers. A strong stabilization upon triplet excitation of the two latter isomers significantly facilitates the interconversions between isomers, and thus considerably reduces the energy barriers for dehydration pathways. The most probable pathways for HCN and HNC generation are found to be dehydration of formamide in the T 1 state. Dehydration pathways from the neutral S 1 and protonated T 1 forms lead to stable complexes of HCN and HNC with water but are associated with large energy barriers. Overall, in the lower-lying excited states of either neutral or protonated formamide, dehydration is not competitive with homolytic C−N bond cleavages, which finally lead to formation of CO.

An ab initio Wannier-function-based approach to electronic groundstate calculations for crystalline solids is outlined. In the framework of the linear combination of atomic orbitals method the infinite character of the solid is rigorously taken into account. The Hartree-Fock groundstate energy, cohesive energy, lattice constant and bulk modulus are calculated in a fully ab initio manner as it is demonstrated for sodium chloride, NaCl, using basis sets close to the Hartree-Fock limit. It is demonstrated that the Hartree-Fock band-structure can easily be recovered with the current approach and agrees with the one obtained from a more conventional Bloch-orbital-based calculation. It is argued that the advantage of the present approach lies in its capability to include electron correlation effects for crystalline insulators by means of well-established quantum chemical procedures.

In the present letter, we report the extension of our Wannier-function-based ab initio Hartree-Fock approach-meant originally for three-dimensional crystalline insulators-to deal with quasi-one-dimensional periodic systems such as polymers. The system studied is all-transoid polyethylene, and results on optimized lattice parameters, cohesive energy and the band structure utilizing 6-31G** basis sets are presented. Our results are also shown to be in excellent agreement with those obtained with traditional Bloch-orbital-based approaches.

This paper reports a theoretical study of the electronic states of PO radical. Highly correlated ab initio methods were used for mapping the potential energy curves. Internally contracted multi-reference configuration interaction method with the augmented correlation-consistent basis set (aV5Z) has been employed to carry out the study. After the nuclear motion treatment, the spectroscopic constants and the vibrational energy levels of the doublet and quartet electronic states are determined. The calculated values have been found in a good agreement with the existing experimental and theoretical results. The spin-orbit couplings between interacting states were also determined in the region where the crossings of the potential energy curves occurs. These couplings are capable to induce predissociation processes involving quartet states and producing P and O atoms at their ground and low lying excited electronic states. The theoretical vibrational spectrum was predicted using the Franck Condon factors and the transition moments integrals. The calculated spectrum shows intense peaks involving the Rydberg states in complete accordance with the experiment.

We have developed and implemented a new ab initio code, Ceres (Computational Emulator of Rare Earth Systems), completely written in C++11, which is dedicated to the efficient calculation of the electronic structure and magnetic properties of the crystal field states arising from the splitting of the ground state spin-orbit multiplet in lanthanide complexes. The new code gains efficiency via an optimized implementation of a direct configurational averaged Hartree-Fock (CAHF) algorithm for the determination of 4f quasi-atomic active orbitals common to all multi-electron spin manifolds contributing to the ground spin-orbit multiplet of the lanthanide ion. The new CAHF implementation is based on quasi-Newton convergence acceleration techniques coupled to an efficient library for the direct evaluation of molecular integrals, and problem-specific density matrix guess strategies. After describing the main features of the new code, we compare its efficiency with the current state-of-the-art...

The adsorption and diffusion of silver adatoms is examined over different partially hydroxylated model a-Al 2 O 3 (0 0 0 1) surfaces created by combinations of quadrants of the two stable phases, a fully hydroxylated surface and the Al-terminated surface. While the model shows relatively weak adsorption which leads to low activation barriers for diffusion, it does not fully capture the behavior observed in XPS experiments by Kelber et al. which report a stronger interaction with the support and an increase in the diffusion barrier when partially hydroxylated surfaces are created. It is suggested that some as of yet uncharacterized defects must be responsible for the observed behavior.

The nuclear dynamics of the chromium carbonyl cation following an ionization process corresponding to the 2T2g ← 1A1g transition is studied theoretically, for the first time, using a fully quantal approach as well as high levels of the ab initio electronic structure and semiempirical density functional theory (DFT) methods. The photoelectron spectrum is calculated by the construction of a Hamiltonian model, in which the two totally symmetric modes ν19 (the Cr-C stretching mode) and ν39 (the C-O stretching mode) together with the spin-orbit (SO) coupling up to the zeroth-order SO splitting are treated. The potential energy curves along these two vibrational modes are computed by using the DFT. The simulated photoelectron spectrum is found to be in good agreement with the corresponding experimental one, leading to the conclusion that the potential energy surfaces and the diabatic population analysis are accurately determined. Our calculation confirms that the vibrational modes ν19 and ν39 are the vibrational progression of the valence ionization spectrum of the chromium carbonyl cation.

Nanostructured doped-ZnO system with various elements (M = Cr, Mn, Fe, Co, Ni, and In) at 10 at.% doping concentration, was investigated. Neutron diffraction refinements confirm the stability of the würztite crystal structure of the parent compound ZnO, the localization of the doping elements within Zn sites, and some residual impurities. Magnetic measurements show a ferromagnetic behavior at room temperature where the magnetic parameters, saturation magnetization (M s), remanence (M r) and coercivity (H c) vary considerable according to the nature of the doping elements, its valence and its solubility level: M s has the highest value of 0.223 emu/g for Ni and lowest value of 0.011 emu/g for Cu. The ab-initio calculations using DFT method confirm the ferromagnetism of doped-ZnO in agreement with magnetic measurements. It is found that oxygen plays an important role to explain the magnetic properties observed in diluted magnetic semiconductors (DMS) of the studied doped-ZnO system. The estimated Curie temperature was found to vary considerably according to the nature of the doping element, with the lowest value for In (105 K) and highest value for Co (737 K).

Size effects on formation energies and electronic structures of oxygen and zinc vacancies in ZnO nanowires: A first-principles study J. Appl. Phys. 109, 044306 (2011); 10.1063/1.3549131 O-vacancy-mediated spin-spin interaction in Co-doped ZnO: First-principles total-energy calculations

Ab initio calculations are becoming increasingly useful to engineers interested in designing new alloys, because these calculations are able to accurately predict basic material properties only knowing the atomic composition of the material. In this paper, single crystal elastic constants of 11 bcc Mg–Li alloys are calculated using density functional theory (DFT) and compared with available experimental data. Based on DFT determined properties, engineering parameters such as the ratio of bulk modulus over shear modulus (B/G) and the ratio of Young’s modulus over mass density (Y/q) are calculated. Analysis of B/G and Y/q shows that bcc Mg–Li alloys with 30–50 at.% Li offer the most potential as lightweight structural material. Compared with fcc Al–Li alloys, bcc Mg–Li alloys have a lower B/G ratio, but a comparable Y/q ratio. An Ashby map containing Y/q vs B/G shows that it is not possible to increase both Y/q and B/G by changing only the composition of a binary alloy.

We studied Structure -Activity Relationships (SAR) of a series of 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine derivatives, which present antispermatogenic activity, using Principal Component Analysis (PCA), K-Nearest Neighbor (KNN) and Neural Network (NN) methods. Firstly, we carried out thorough conformational explorations using the PM3 method, in order to determine the most stable conformations. The minima found were optimized using ab initio HF/3-21G. Molecular properties were calculated using the same ab initio method. Steric properties such as molecular volume and surface and the octanol/water partition coefficient were also calculated. A total of three variables (atomic charges on two specific atoms and the molecular volume) out of many were selected as being useful for SAR. PCA yielded a reasonable separation between high-activity and low-activity groups. The KNN and NN methods presented approximately 70% correct classifications. Finally, a set of new compounds was proposed and analyzed. q