First-principles calculations of structural and thermodynamic properties of BeB2 compound

The lattice parameter bulk modulus and pressure derivative of BeB2 are calculated by using the Cambridge Serial Total Energy Package （CASTEP） program in the frame of density function theory. The calculated results agree well with the average experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/ao, c/c0 and the normalized primitive cell volume V/Vo on pressure P, the variation of the thermal expansion coefficient ~ with pressure P and temperature T, as well as the dependences of the heat capacity Cv on pressure P and temperature T are obtained systematically.

Phase transition and thermodynamic properties of TiO_2 from first-principles calculations

The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method （DFT）, together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92 GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/Vo on pressure and the dependences of thermal expansion coefficient α on temperature and pressure are also obtained successfully.

Elastic and thermodynamic properties of c-BN from first-principles calculations

The elastic constants and thermodynamic properties of c-BN are calculated using the first-principles plane wave method with the relativistic analytic pseudopotential of the Hartwigen, Goedecker and Hutter （HGH） type in the frame of local density approximation and using the quasi-harmonic Debye model, separately, Moreover, tbe dependences of the normalized volume V/V0 on pressure P, as well as the bulk modulus B, the thermal expansion α, and the heat capacity CV on pressure P and temperature T are also successfully obtained,

Structural and thermodynamic properties of AlB2 compound

We employ a first-principles plane wave method with the relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter （HGH） scheme in the frame of DFT to calculate the equilibrium lattice parameters and the thermodynamic properties of AlB2 compound with hcp structure. The obtained lattice parameters are in good agreement with the available experimental data and those calculated by others. Through the quasi-harmonic Debye model, obtained successfully are the dependences of the normalized lattice parameters α/αo and c/co on pressure P, the normalized primitive cell volume V/Vo on pressure P, the variation of the thermal expansion α with pressure P and temperature T, as well as the Debye temperature OD and the heat capacity Cv on pressure P and temperature T.

Electronic structures and optical properties of monoclinic ZrO2 studied by first-principles local density approximation plus U approach

The electronic structures and optical properties of the monoclinic ZrO2 (m-ZrO2) are investigated by means of first-principles local density approximation (LDA) + U approach.Without on-site Coulomb interactions,the band gap of m-ZrO2 is 3.60 eV,much lower than the experimental value (5.8 eV).By introducing the Coulomb interactions of 4d orbitals on Zr atom (Ud) and of 2p orbitals on O atom (Up),we can reproduce the experimental value of the band gap.The calculated dielectric function of m-ZrO2 exhibits a small shoulder at the edge of the band gap in its imaginary part,while in the tetragonal ZrO2 and cubic ZrO2 it is absent,which is consistent with the experimental observations.The origin of the shoulder is attributed to the difference of electronic structures near the edge of the valence and conduction bands.

Structural,thermodynamic and electronic properties of zinc-blende AlN from first-principles calculations

Structural, thermodynamic and electronic properties of zinc-blende AIN under pressure are investigated by first- principles calculations based on the plane-wave basis set. Through the analysis of enthalpy variation of AIN in the zinc-blende （ZB） and the rock-salt （RS） structures with pressure, we find the phase transition of A1N from ZB to RS structure occurs at 6.7GPa. By using the quasi-harmonic Debye model, we obtain the heat capacity Cv, Debye temperature θD, Gruneisen parameter γ and thermal expansion coefficient α. The electronic properties including fundamental energy gaps and hydrostatic deformation potentials are investigated and the dependence of energy gaps on pressure is analysed.

First Principle Study of the Structural and Piezoelectric Properties of Perovskite ZrTi(PbO₃)₂Materials for Naval SONAR

First principle calculation within the Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) using Local Density Approximation as implemented in Quantum ESPRESSO has been significantly used to investigate the structural and Piezoelectric, properties of Perovskite ZrTi(PbO3)2. From structural properties calculation, the ground state total energy of -2417.12 eV has been obtained which led to an equilibrium lattice constant of a= 5.620Åfor ZrTi(PbO3)2. Our obtained optimized atomic positions and atomic effective charge shows that the optimized ZrTi(PbO3)2 is stable and the Piezoelectric stress tensor is calculated using Berry-phase approach within density functional perturbation theory (DFPT). From our calculation, we have obtained the stress tensor elements with values of d1,5 = 6.81, d3,1 = 1.69, and d3,3 = 6.18, which is in agreement with the values obtained for tetragonal PbTiO3.

高压下碳化钛热力学性质的第一性原理计算

碳化钛熔点高、硬度高、化学性能稳定性好,工业上主要用来制造金属陶瓷、耐热合金和硬质合金.采用平面波密度泛函理论广义梯度近似计算了碳化钛的弹性常数、晶格常数、体积模量,所得结果与实验和其它理论值相一致;通过准谐德拜模型预测了碳化钛的相对体积与压强,体积模量分别与压强和温度,热容与温度的变化关系,结果表明:温度对体积模量的影响远小于压强对体积模量的影响.该研究对碳化钛在高温高压下的应用具有指导意义.

均匀重力场中弱相互作用费米气体的热力学性质

根据局域密度近似法,研究了均匀重力场中弱相互作用费米气体高于费米温度条件下的性质,得到了一些重要热力学量的一般解析表达式,分析了系统的粒子数和能量密度的空间分布规律。对均匀重力场中理想费米体系,均匀重力场中弱相互作用费米体系进行了比较,探讨了重力势场及粒子间的相互作用对体系性质的影响。