Gou Qing-Quan

Phase Transition and Phonon Spectrum of Zinc-Blende Structure ZnX (X = S, Se, Te)

Calculations have been performed to investigate the pressure-induced solid-solid phase transitions and the mechanical stability for three zinc-blende II-VI semiconductor compounds: ZnS, ZnSe, ZnTe by ab initio plane-wave pseudopotential density functional theory (DFT). Using the generalized gradient approximation (GGA) for exchange and correlation in the scheme of Perdew-Wang 1991 (PW91), the ground state properties and equation of state are obtained, which are well consistent with the experimental data available and other calculations. On the basis of the forth-order Birch-Murnaghan equation of states, the transition pressures P(t) are determined through the analysis of enthalpy variation with pressure. A linear-response approach is used to calculate the frequencies of the phonon dispersion. Finally, by the calculations of phonon frequencies, some thermodynamic properties such as the vibrational contribution to the Helmholtz free energy (F), enthalpy (H), entropy (S), and the heat capacity (C(V)) are also successfully obtained

First-Principle Calculations for Elastic and Thermodynamic Properties of Diamond

The elastic constants and thermodynamic properties of diamond are investigated by using the CRYSTAL03 program. The lattice parameters, the bulk modulus, the heat capacity, the Gruneisen parameter, and the Debye temperature are obtained. The results are in good agreement with the available experimental and theoretical data. Moreover, the relationship between V/V(0) and pressure, the elastic constants under high pressure are successfully obtained. Especially, the elastic constants of diamond under high pressure are firstly obtained theoretically. At the same time, the variations of the thermal expansion a with pressure P and temperature Tare obtained systematically in the ranges of 0-870 GPa and 0-1600 K.

First-Principle Calculations for Transition Phase and Elastic Properties of SrS

The transition phase and elastic properties of SrS from NaCl structure (B1) to CsCl structure (B2) are investigated by ab initio plane-wave pseudopotential density functional theory method and by the quasi-harmonic Debye model. The transition pressure varies non-linearly with temperature, and the pressure of the mechanical instability increases linearly with increasing temperature. It is shown that the B1 structure SrS is a most elastically anisotropic mineral at any pressure. The Debye temperature, the heat capacity, thermal expansion and Gruneisen parameter over a wide range of pressures and temperatures are also obtained.

Elastic and Thermodynamic Properties of CdSe from First-Principles Calculations

The lattice parameters, bulk modulus, phase transition pressure, and temperature dependencies of the elastic constants cij of CdSe are investigated by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of Density Functional Theory (DFT). It is found that the phase transitions from the ZB structure to the RS structure and from WZ structure to RS structure are 2.2 GPa and 2.8 GPa, respectively. Our results agree well with the available experimental data and other theoretical results. The aggregate elastic modulus (B, G, E, A), the Poissons ratio (υ), the Gruneisen parameter (γ), the Debye temperature ΘD on pressure and temperature are also successfully obtained.

Electronic and Optical Properties of Rock-Salt AlN under High Pressure via First-Principles Analysis

Electronic and optical properties of rock-salt AlN under high pressure are investigated by first -principles method based on the plane-wave basis set. Analysis of band structures suggests that the rock-salt AlN has an indirect gap of 4.53 eV, which is in good agreement with other results. By investigating the effects of pressure on the energy gap, the different movement of conduction band at X point below and above 22.5 GPa is predicted. The optical properties including dielectric function, absorption, reflectivity, and refractive index are also calculated and analyzed. It is found that the rock-salt AlN is transparent from the partially ultra-violet to the visible light area and hardly does the transparence affected by the pressure. Furthermore, the curve of optical spectrum will shift to high energy area (blue shift) with increasing pressure.

Shell Model for Elastic and Thermodynamic Properties of Gallium Nitride with Hexagonal Wurtzite Structure

Shell model molecular dynamic simulation with interatomic pair potential is utilized to investigate the elastic and thermodynamic properties of gallium nitride with hexagonal wurtzite structure (w-GaN) at high pressure. The calculated elastic constants Cij at zero pressure and 300 K agree well with the experimental data and other calculated values. Meanwhile, the dependences of the relative volume V/V0, elastic constants Cij, entropy S, enthalpy H, and heat capacities CV and CP on pressure are successfully obtained. From the elastic constants obtained, we also calculate the shear modulus G, bulk modulus B, Youngs modulus E, Poissons ratio v, Debye temperature D, and shear anisotropic factor Ashear on pressures.

First-Principle Calculations for Thermodynamic Properties of LiBC Under High Temperature and High Pressure

The thermodynamic properties of LiBC are investigated by using the full-potential linearized muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT) and using the quasi-harmonic Debye model. The dependencies of the normalized lattice parameters a/a0 and c/c0, the ratio (c/a)/2, the normalized primitive volume V/V0 on pressure and temperature are successfully obtained. It is found that the interlayer covalent interactions (Li-B bonds or Li-C bonds) are more sensitive to temperature and pressure than intralayer ones (B-C bonds), as gives rise to the extreme lattice anisotropy in the bulk hcp LiBC.

Phonon Dispersion and Thermodynamics Properties of CaF2 via Shell Model Molecular Dynamics Simulations

The phonon and thermodynamics properties of face-centered cubic CaF2 at high pressure and high temperature are investigated by using the shell model interatomic pair potential within General Utility Lattice Program (GULP). The phonon dispersion curves and the corresponding density of state (PDOS) in this work are consistent with the experimental data and other theoretical results. The transverse optical (TO) and longitudinal optical (LO) mode splitting as well as heat capacity at constant volume CV and entropy S versus pressure and temperature are also obtained.

Structural and Thermodynamic Properties of Cerium via First-Principles Plane Wave Method with a Relativistic Analytic Pseudopotential

We investigate the structural and thermodynamic properties of cerium in.. phase by using the first-principles plane wave method with a relativistic analytic pseudopotential of Hartwigsen, Goedcker and Hutter (HGH) scheme in the frame of local density approximation (LDA). The obtained lattice constant and bulk modulus are consistent with the available experimental data. Moreover, dependences of the normalized primitive volume V/V(0) on pressure and the thermodynamic quantities ( including the Gruneisen constant gamma and thermal expansion alpha) on temperature and pressure are obtained. The obtained linear thermal expansion parameter alpha (9.857 x 10(-6) K(-1) at 293.15 K and 0 GPa) is slightly larger than the experimental value (6.3 x 10(-6) K(-1)). All the results indicate that we provide an effective method to deal with the ground properties of the strongly interacting d- and/or f-electron systems.

First-Principle Calculations for Scanning-Tunnelling-Microscopic Images of a Monolayer Graphite Surface

We have applied first-principle total-energy electronic structure calculations in the local density approximation to calculate the scanning tunnelling microscopy images of a monolayer graphite surface near the Fermi level. The results obtained agree well with the observation, which has not been interpreted before.