Elastic Constants of NaC1 under Pressure via First-Principles Calculations

The elastic constants of the B1 structure NaCl under pressure are obtained by using the ab initio plane-wave pseudopotential density functional theory method. The obtained zero pressure lattice constant and elastic constants are in good agreement with the available experimental data. It is found that the elastic constants C11 and C12 and the bulk modulus B increase monotonically with pressure P, however C44 increases monotonically when P_〈28 GPa and decreases when P〉28 GPa. Moreover, we discuss the B1-B2 structure phase transition of NaCl and obtain the transition pressure of 28.3 GPa.     

Ab Initio Calculations of Phonon Spectra in BaF2 and PbF2 Crystals

Russian Physics Journal - The density functional theory is used to calculate vibrational spectra, suggest dependencies of total energies and frequencies on BaF2 and PbF2 crystal lattice constants,...     

Structure Formation of Hexagonal Diamond: Ab Initio Calculations

Physics of the Solid State - The formation of structure of hexagonal diamond from graphite and cubic diamond is simulated with the density functional theory. Orthorhombic AB graphite transforms...     

First-Principles Calculations for Elastic Properties of ZnS under Pressure

The pressure dependence of elastic properties of ZnS in zinc-blende （ZB） and wurtzite （WZ） structures are investigated by the generalized gradient approximation （GGA） within the plane-wave pseudopotential density functional theory （DFT）. Our results are in good agreement with the available experimental data and other theoretical results. From the high-pressure elastic constants obtained, we find that the ZB and WZ structures of ZnS are unstable when the applied pressures are larger than 15.8 GPa and 21.3 GPa, respectively. The sound velocities along different directions for the two structures are also obtained. It is shown that as pressure increases, the sound velocities of the shear wave decrease, and those of all the longitudinal waves increase. An analysis has been made to reveal the anisotropy and highly noneentral forces in ZnS.     

Ab Initio Calculations for the Polarizabilities of Small Sulfur Clusters

Polarizabilities of small Sn （n = 2-8） clusters are calculated by using the higher-order finite-difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters are considered to be higher than the value estimated from the “hard sphere” model using the bulk static dielectric constant. The computed polarizabilities per atom tend to decrease with the increasing cluster size. The polarizabilities are closely related to the HOMO-LUMO gaps and the geometrical configurations.     

First-Principles Calculations of Structural,Elastic and ElectronicProperties of Tetragonal HfO2under Pressure

Structural, elastic and electronic properties of tetragonal HfO₂ at applied hydrostatic pressure up to 50 GPa have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated ground-state properties are in good agreement with previous theoretical and experimental data. Six independent elastic constants of tetragonal HfO₂ have been calculated at zero pressure and high pressure. From the obtained elastic constants, the bulk, shear and Young's modulus, Poisson's coefficients, acoustic velocity and Debye temperature have been calculated at the applied pressure. Band structure shows that tetragonal HfO₂ is an indirect band gap. The variation of the gap versus pressure is well fitted to a quadratic function.     

First-Principles Calculations about Elastic and Li+ Transport Properties of Lithium Superoxides under High Pressure and High Temperature

Lithium superoxides,Li2O3,LiO2,and LiO4,have been synthesized under high pressure.These materials have potential applications in energy storage devices.Here,we ...     

Phonon Spectrum of Eu2Sn2O7: Ab Initio Calculation

Optics and Spectroscopy - The crystal structure and phonon spectrum of a Eu2Sn2O7 crystal is studied within the MO–LCAO approach using the hybrid DFT functional, which takes into account the...     

Phonon Spectrum of La2Ge2O7: Ab Initio Calculation

Physics of the Solid State - Within the density functional theory, ab initio calculation of the crystal structure, phonon spectrum, and elastic properties of lanthanum germanate La2Ge2O7 with...     

Theoretical Calculations for Structural, Elastic and Thermodynamic Properties of MgB2 under High Pressure

We have investigated the structural and elastic properties of MgB₂ under high pressures using the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory. The calculated pressure dependence of the normalized volume is in excellent agreement with the experimental results. At the same time the elastic constants and acoustic anisotropy as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of MgB₂.     

Ab Initio Calculations and Raman and SERS Spectral Analyses of Amphetamine Species

Abstract

For the first time, the differences between the spectra of amphetamine and amphetamine-H⁺ and between different conformers are thoroughly studied by ab initio model calculations, and Raman and surface-enhanced Raman spectroscopy (SERS) spectra are measured for different species of amphetamine. The spectra of amphetamine and amphetamine-H⁺ samples were obtained and assigned according to a comparison of the experimental spectra and the ab initio MO calculations, performed using the Gaussian 03W program (Gaussian, Inc., Pittsburgh, PA). The analyses were based on complete geometry minimization of the conformational energy of the S-plus-amphetamine molecule and the S-plus-amphetamine-H⁺ ion. The harmonic frequency calculations provide information about the characteristic features of the Raman spectra and the nature of the bonding in the molecule. It is concluded that vibrational bands from salt anions with internal bonds (sulfates, hydrogen phosphates, etc.) need to be taken into account when employing these spectra for identification purposes. These results also show how Raman spectroscopy can assist the forensic community in drug profiling studies. Furthermore, because their spectra are different, discrimination between the free and protonated forms of amphetamine salts can be observed. Here, we provide evidence for this difference and show experimentally how it has been overseen.     

Ab Initio SCF Calculations Relating to the Cls Chemical Shifts for Some Alkanes

Ab initio calculatios have been made for a series of simple alkanes and the atomic charges have been estimated in two ways, using the Mulliken population analysis and also using an analysis due to Karlström where the charges are fitted to describe the electrical moments derived from the SCF wave function. Also the orbital energies were calculated. The results were used to interpret experimental data of the carbon core electron binding energies. It is found that the Karlström technique is best suited to describe the XPS data.     

Ab Initio Calculations of the Electronic Properties and the Transport Phenomena in Graphene Materials

Physics of the Solid State - The density functional theory (DFT) is used to study the electronic properties and the energy structure of monolayers of graphene supercells consisting of 18 and 54...     

Ab Initio Study of Structural,Electronic, and Elastic Properties of Graphene

Physics of the Solid State - Since its discovery in 2004, graphene has attracted the intention of several researchers in the world because of its fascinating electronic and mechanical properties....     

Electronic Structure of Transition-Metal Pnictide Oxides La3T4As4O2 (T = Ni,Cu) from Ab Initio Calculations

JETP Letters - The electronic structure of the recently synthesized compounds La3T4As4O2 (T = Ni, Cu) are studied using the ab initio APW + lo method. A careful analysis of band structures and...