Structural,electronic,vibrational,and thermodynamic properties of Zr_(1-x)Hf_xCo:A first-principles-based study

The physical properties including structural,electronic,vibrational and thermodynamic properties of Zr1-xHfx Co(x is the concentration of constituent element Hf,and changes from 0 to 1) are investigated in terms of the ABINIT program.The results reveal that all of Zr_(1-x)Hf_x Co have similar physical properties.When Hf concentration x gradually increases from 0.0 to 1.0,the lattice constant decreases from 3.217 ?A to 3.195 ?A very slowly.The calculated density of states(DOS)indicates that the metallic nature is enhanced and the electrical conductivity turns better with the increase of Hf.Moreover,as Hf concentration increases from 0 to 1,the Fermi energy gradually increases from-6.96 e V to-6.21 e V,and the electronic density of states at the Fermi level(N(E_f)) decreases from 2.795 electrons/e V f.u.down to 2.594 electrons/e V f.u.,both of which imply the decrease of chemical stability.The calculated vibrational properties show that the increase of Hf concentration from 0 to 1 causes the maximum vibrational frequency to decrease gradually from about 223 cm~(-1) to 186 cm~(-1),which suggests a lower dispersion gradient and lower phonon group velocities for these modes.Finally,the phonon related thermodynamic properties are obtained and discussed.     

Elastic,vibrational, and thermodynamic properties of Sr_(10)(PO_4)_6F_2 and Ca_(10)(PO_4)_6F_2 from first principles

The electronic, elastic, vibrational, and thermodynamic properties of Sr_(10)(PO_4)_6F_2(Sr-FAP) and Ca_(10)(PO_4)_6F_2(CaFAP) are systematically investigated by the first-principles calculations. The calculated electronic band structure indicates that the Sr-FAP and Ca-FAP are insulator materials with the indirect band gap of 5.273 eV and 5.592 eV, respectively. The elastic constants are obtained by the "stress–strain" method, and elastic modulus are further evaluated and discussed. The vibrational properties, including the phonon dispersion curves, the phonon density of states, the Born effective charge, and associated longitudinal optical and transverse optical(LO–TO) splitting of optical modes, as well as the phonon frequencies at zone-center are obtained within the linear-response approach. Substitution of Ca by Sr causes phonon frequencies to shift to lower values as expected due to the mass effect. Additionally, some phonon-related thermodynamic properties, such as Helmholtz free energy F, internal energy E, entropy S, and specific heat C_V of Sr-FAP and Ca-FAP are predicted with the harmonic approximation. The present calculated results of two apatites are consistent with the reported experimental and theoretical results.     

Lattice dynamics properties of chalcopyrite ZnSnP_2:Density-functional calculations by using a linear response theory

We present a first-principles study of the structural,dielectric,and lattice dynamical properties for chalcopyrite semiconductor ZnSnP_2.The structural properties are calculated using a plane-wave pseudopotential method of densityfunctional theory.A linear response theory is used to derive Born effective charge tensors for each atom,dielectric constants in low and high frequency limits,and phonon frequencies.We calculate all zone-center phonon modes,identify Raman and infrared active modes,and report LO-TO splitting of the infrared modes.The results show an excellent agreement with experiment and propose several predictive behaviors.     

CdGeAs2单晶体的腐蚀研究

报道了一种新型的CdGeAs2晶体择优腐蚀剂,配方为:H2O2(30;): NH4OH(含NH325;-28;): NH4Cl(5mol/L): H2O=1 mL: 1.5 mL: 1.5 mL: 2 mL.将经机械研磨、物理抛光和溴甲醇化学抛光处理后的表面平整无划痕的CdGeAs2晶片,在40 ℃下超声振荡腐蚀数分钟,采用金相显微镜和SEM进行蚀坑观察.结果表明,新型腐蚀剂对CdGeAs2晶体(204)和(112)晶面择优腐蚀效果显著,蚀坑取向一致,具有很强的立体感;(204)晶面蚀坑呈三角锥形,(112)晶面蚀坑呈五边形,从晶体结构上对蚀坑形成机理进行了分析讨论.     

Mechanical and Vibrational Properties of ZnS with Wurtzite Structure： A First-Principles Study

We perform a first-principles study of the mechanical and vibrational properties of ZnS with a wurtzite structure. The calculated elastic constants by using a pseudopotential plane-wave method agree well with the experimental data and with the previous theoretical works. Based on the elastic constants and their related parameters, the crystal mechanical stability is discussed. Calculations of the zone-center optical-mode frequencies including longitudinal-optical/transverse-optical splitting, by using the density functional perturbation theory, are reported. All optical modes are identified, especially B1 modes, and agree with Raman rneasurements.     

Potential energy curves,transition dipole moments,and radiative lifetimes of KBe molecule

An ab initio calculations on the ground and low-lying excited states(X~2Σ+, 2~2Σ+, 3~2Σ+, 1~4Π, 2~4Π, 1~4Σ~+, 2~4Σ~+,and 3~4Σ~+) of KBe molecule have been performed using multireference configuration interaction(MRCI) plus Davidson corrections(MRCI+Q) approach with all electron basis set aug-cc-p CV5Z-DK for Be and def2-AQZVPP-JKFI for K.The 3~2Σ+, 1~4Π, 2~4Π, 1~4Σ~+, 2~4Σ~+, and 3~4Σ~+states are investigated for the first time. Inner shell electron correlations are computed on the potential energy curves(PECs) calculations. The spectroscopic and molecular parameters are also predicted. In addition, The transition properties including transition dipole moment, Franck–Condon factors qv'v', Einstein coefficients Av'v', and the radiative lifetimes τυ for the 2~2Σ~+–X~2Σ~+, 3~2Σ~+–X~2Σ~+, and 2~4Π–1~4Π transitions are predicted at the same time.     

First-principles calculations of structure and elasticity of hydrous fayalite under high pressure

The structures,elasticities,sound velocities,and electronic properties of anhydrous and hydrous fayalite(Fe_2SiO_4and Fe_(1.75)H_(0.5)SiO_4)under high pressure have been investigated by means of the density functional theory within the generalized gradient approximation(GGA)with the on-site Coulomb energy being taken into account(GGA+U).The optimized results show that H atoms prefer to substitute Fe atoms in the Fe1 site.Compared with the anhydrous fayalite Fe_2SiO_4,the mass density,elastic moduli,and sound velocities of Fe_(1.75)H_(0.5)SiO_4 slightly decrease.According to our data,adding 2.3 wt%water into fayalite leads to reductions of compressional and shear wave velocities(VPand VS)by3.4%–7.5%and 0.3%–3.4%at pressures from 0 GPa to 25 GPa,respectively,which are basically in agreement with the2%–5%reductions of sound velocity obtained by the experimental measurement in the low velocity zones(LVZ).Based on the electronic structure,the valence and conduction bands are slightly broader for hydrous fayalite.However,hydrous fayalite keeps the insulation characteristics under the pressures up to 30 GPa,which indicates that hydration has little effect on its electronic structure.