氮化铂在高压下的相变及弹性性质的第一原理计算

用PBE形式下的广义梯度近似（GGA）赝势平面波方法研究了氮化铂的结构相变以及弹性性质,计算了氮化铂的氯化钠（B1）、氯化铯（B2）、闪锌矿（B3）、纤维矿（B4）等四种结构并应用高压下的焓与压强的关系,得出在常温常压下B4结构是最稳定的结构,这与Yu 等人得的结果一致,且 B4→B1及B1→B2的相变压强分别发生在36.7 GPa和 185.4 GPa,同时,研究了B4结构在高压的弹性性质,发现弹性常数、体模量、剪切模量、压缩波速、剪切波速以及德拜温度均随着压强的增大而单调增大     

氮化铂在高压下的相变及弹性性质的第一原理计算

用PBE形式下的广义梯度近似（GGA）赝势平面波方法研究了氮化铂的结构相变以及弹性性质，计算了氮化铂的氯化钠（B1）、氯化铯（B2）、闪锌矿（B3）、纤维矿（B4）等四种结构并应用高压下的焓与压强的关系，得出在常温常压下B4结构是最稳定的结构，这与Yu 等人得的结果一致，且 B4→B1及B1→B2的相变压强分别发生在36.7 GPa和 185.4 GPa，同时，研究了B4结构在高压的弹性性质，发现弹性常数、体模量、剪切模量、压缩波速、剪切波速以及德拜温度均随着压强的增大而单调增大     

加压下ZnO结构相变和电子结构的第一性原理计算

基于密度泛函(DFT)理论的第一性原理,计算半导体ZnO纤锌矿结构和岩盐矿结构状态方程及其在高压下的相变,分析加压下体相ZnO的晶格常数、电子态密度和带隙随压力的变化关系,并将计算结果与文献中的理论和实验数据进行比较.验证在计算金属氧化物时,应用局域密度(LDA)近似计算出的相变压力普遍偏高,采用广义梯度(GGA)近似得到的结果与实验符合较好.     

高压下氧化镉弹性性质、电子结构和光学性质的第一性原理研究

 运用基于密度泛函理论的平面波赝势方法（PWP）,计算研究了氧化镉NaCl结构（B1结构）和CsCl结构（B2结构）在不同压力条件下的几何结构、弹性性质、电子结构和光学性质。交换关联能分别采用广义梯度近似（GGA）和局域密度近似（LDA）。通过比较计算和实验得到的晶格常数和体模量不难发现,LDA的计算结果更符合实验值。在高压的作用下,两种结构的导带能级有向高能级移动的趋势,而价带能级有向低能级移动的趋势,因此直接带隙变大。同时,对照态密度分布图及高压下能级的移动情况,分析了CdO两种结构在高压作用下的光学性质。     

第一性原理对金的高压相变和零温物态方程的计算

在密度泛函理论下，用缀加平面波加局域轨道方法，分别采用广义梯度近似(GGA)和局域密度近似(LDA)对金的面心立方晶格结构(fcc)、体心立方晶格结构(bcc)和六角密堆积结构(hcp)的结构能量进行了计算.在GGA下，计算得出fcc向hcp和hcp向bcc的相变分别发生在380GPa 和1250GPa；而LDA下相变分别发生在490GPa和790GPa.当计算压强达到2TPa时，bcc在这两种近似下仍然保持稳定的结构.根据不同体积下不同结构的电子态密度的特征，对发生相变的物理原因进行了定性的分析，在此基础上得到了金的零温状态方程. 关键词： 缀加平面波方法 固态相变 电子态密度 物态方程     

航天新材料金属锆的压缩行为

在密度泛函理论的基础上,运用局域密度近似(LDA)和广义梯度近似(GGA)两种方法,并通过第一性原理等方法对锆晶体在0～50 GPa下的物理性质进行了深入、系统的研究.结果表明,相比于广义梯度近似的计算结果而言,局域密度近似的计算结果和实验值更接近,但两者相差不是很大.并通过经典方法对锆晶体模拟计算了高压下的结构性质,得到的结果表明,在讨论的压强范围内,晶格参数与晶胞体积发生了非线性的变化,然而晶胞能量却随压强线性变化.通过对其相应的弹性性质的分析,发现随着压强的增大,锆晶体获得较好的延展性以及力学的稳定性.同时还得到了关于金属锆的能带结构特性及其光学性质,证实压强的改变对金属锆电子性质不会带来太大影响.     

第一性原理计算航天新材料金属锆的压缩行为

在密度泛函理论的基础上,运用局域密度近似(LDA)和广义梯度近似(GGA)两种方法,并通过第一性原理等方法对锆晶体在0到50GPa下的物理性质进行了深入、系统的研究。结果表明,相比于广义梯度近似的计算结果而言,局域密度近似的计算结果和实验值更接近,但两者相差不是很大。并通过经典方法对锆晶体模拟计算了高压下的结构性质,得到的结果表明,在讨论的压强范围内,晶格参数与晶胞体积发生了非线性的变化,然而晶胞能量却随压强线性变化。通过对其相应的弹性性质的分析,发现随着压强的增大,锆晶体获得较好的延展性以及力学的稳定性。同时还得到了关于金属锆的能带结构特性及其光学性质,证实压强的改变对金属锆电子性质不会带来太大影响。     

0～15 GPa外压下ZnO结构相变的第一性原理研究

利用第一性原理的计算方法,结合热力学和弹性力学的计算详细分析0～15 GPa外压下ZnO的结构、弹性模量和电子结构.结果表明:在研究压强范围内,B4结构的ZnO能量始终比B3结构的低,但随着外压的增加,无论是B4结构还是B3结构,都会在一定压强下转变成B1结构.B4至B1的压强转变点为12.4 GPa,B3至B1的压强转变点是11.8 GPa.B4结构转变成B1结构的瞬间,体系体积缩小约17%.结果与已有的实验与理论结果相符.B4结构的ZnO剪切模量在6～8 GPa时急剧下降,与已有的实验和理论计算结果相符.电子结构特征表明,随着外压的增强,体系中Zn 3d电子与O 2p电子相互作用减弱.     

ZnSe相变、电子结构的第一性原理计算

基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,对闪锌矿结构(ZB)和岩盐结构(RS)的ZnSe在0—20GPa高压下的几何结构、态密度、能带结构进行了计算研究,分析了闪锌矿结构ZnSe和岩盐结构ZnSe的几何结构.在此基础上,研究了ZnSe的结构相变、弹性常数、成键情况以及相变压强下电子结构的变化机理.结果发现:通过焓相等原理得到的ZB相到RS相的相变压强为15.3GPa,而由弹性常数判据得到的相变压强为11.52GPa,但在9.5GPa左右并没有发现简单立方相的出现;在结构相变过程中,sp3轨道杂化现象并未消除,Zn原子的4s电子在RS相ZnSe的导电性中起主要贡献.     

高压下钒的结构相变及熔化温度的第一性原理计算

本文基于第一性原理的密度泛函理论（DFT）和密度泛函微扰理论（DFPT）,优化计算出金属钒在不同压强下的晶体结构,以此来说明其发生的结构相变。最后利用晶体结构和能量的关系,直接导出钒在不同压强下的熔化温度。计算结果都与已有的结果进行了比较。     

Structural phase stability,elastic parameters and thermal properties of YN from first-principles calculation

The structural phase stability, elastic parameters and thermodynamic properties of YN at normal and under high pressure are reported. The calculations are mainly performed using the full-potential linearized augmented plane wave method within the density functional theory. Both local density approximation (LDA) and generalized gradient approximation (GGA) are used to model the correlation-exchange potential. The calculated equilibrium lattice parameter and the bulk modulus show good accordance with the experimental and previous theoretical reports. The phase transition from the NaCl (B1) structure to the CsCl (B2) structure is found to occur at 131?GPa within GGA and 115?GPa within LDA. The linear pressure coefficients of the different elastic moduli being addressed here are also determined along with the mechanical and dynamical stability criteria which are shown to be satisfied for YN with B1 phase under normal conditions. Besides, the heat capacity and other thermodynamic parameters are examined and discussed versus temperature.     

Ab initio lattice dynamics and thermodynamic properties of SrO under pressure

We present an ab initio calculation of lattice dynamics and thermodynamic properties of SrO in the NaCl (B1) and CsCl (B2) structured phases under pressure. We employ the density-functional perturbation theory (DFPT) within the local density approximation (LDA) in conjunction with the quasi-harmonic approximation. At zero pressure, the calculated dispersions agree well with the measured ones for the B1 phase. A pressure-induced soft transverse acoustic (TA) phonon mode is identified at the zone boundary X point of the Brillouin zone. The B2 phase is stable at high pressure. Our analysis suggest that this soft transverse mode is responsible for the pressure induced structural phase transition. The increase of the electronic dielectric function with pressure is attributed to the closure of the p–d gaps. The thermal expansion coefficient decreases with pressure and does not show any negative behavior. The predicted transition pressure decreases with temperature.     

Structural phase transition and elastic properties of Curium and Uranium monobismuthides under pressure effect

A density functional (DFT) calculations of the structural, elastic and high pressure properties of the cubic XBi (X=U,Cm) compounds, has been reported using the full potential linear muffin-tin orbital (FP-LMTO) method. In this approach the local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus and its pressure derivatives. The pressure transitions at which these compounds undergo structural phase transition from NaCl-type (B1) to CsCl-type (B2) phase were found to be in good agreement with the available theoretical results. We have determined the elastic constants C₁₁, C₁₂, C₄₄ and their pressure dependence which have not been established experimentally or theoretically.     

Effect of hydrostatic pressure on the structural, elastic and electronic properties of (B3) boron phosphide

In this paper we present the results obtained from first-principles calculations of the effect of hydrostatic pressure on the structural, elastic and electronic properties of (B3) boron phosphide, using the pseudopotential plane-wave method (PP-PW) based on density functional theory within the Teter and Pade exchange-correlation functional form of the local density approximation (LDA). The lattice parameter, molecular and crystal densities, near-neighbour distances, independent elastic constants, bulk modulus, shear modulus, anisotropy factor and energy bandgaps of (B3) BP under high pressure are presented. The results showed a phase transition pressure from the zinc blende to rock-salt phase at around 1.56?Mbar, which is in good agreement with the theoretical data reported in the literature.     

Effect of high pressure on polymorphic phase transition and electronic structure of XAs (X=Al,Ga, In)

The structural and electronic properties of XAs (X = Al, Ga, In) under pressure have been investigated using ab-initio pseudo-potential approach within local density approximation in B3→B1→B2 phases. The values of phase transition pressures show reasonably good agreement with the experimental data and better than others. The B1→B2 phase transition in InAs is not seen. The volume collapse computed from equation of state (EOS) is found to be in good agreement with the experimental values. Under ambient conditions, the energy of B3 phase is lowest as compared to other phases, while at high pressures beyond B1→B2 phase transition, the energy of B2 phase is found to be lower than that of B1 phase showing correct stability of the phases. There is relatively smaller enthalpy associated with B3→B1 transition as compared to B3→B2 transition. The electronic structures have also been computed at different pressures. We have also reported the effect of pressure on energy gap and valence band width.     

Structural and electronic properties of ZnO under high pressures

In this work, we use first-principles calculations based on density-functional theory within the local-density approximation (LDA) to investigate the structural and electronic properties of ZnO under high-pressure. We have calculated the ground-state energy, the lattice constant, the bulk modulus, and its pressure derivative of the B4 (wurtzie), B3 (zinc blende), B2 (CsCl) and B1 (rocksalt) phases of ZnO. Moreover, the electronic structure, density of states (DOS) of the B4 (wurtzite) and B1 (rocksalt) phases of ZnO have been calculated. We show that our calculated values compare acceptably well with values reported in the literature.     

High pressure study of structural and electronic properties of magnesium telluride

The full-potential linear muffin-tin orbital method (FP-LMTO) within the local density approximation (LDA) is used to calculate the electronic band structures and the total energies of MgTe in its stable (NiAs-B8) and high pressure phases. The latter provide us with the ground state properties such us lattice parameter, bulk modulus and its pressure derivatives. The transition pressure at which this compound undergoes the structural phase transition from the NiAs to CsCl phase is calculated. The energy band gaps and their volume and pressure dependence in the stable NiAs-B8 phase are investigated. The ground state properties, the transition pressure are found to agree with the experimental and other theoretical results. The elastic constants at equilibrium in both NiAs and CsCl structure are also determined.     

Density functional study of optical properties of beryllium chalcogenides compounds in nickel arsenide B8 structure

The structural, electronic and optical properties of beryllium chalcogenides BeS, BeSe and BeTe using the full-potential linear augmented plane wave (FP-LAPW) method are investigated. The exchange-correlation energy within the local density approximation (LDA) and the generalized gradient approximation (GGA) are described. The Engel-Vosko (EVGGA) formalism is applied for electronic and optical properties. The structural parameters of our model and the transition pressure from zinc-blende (B3) to the NiAs (B8) phase are confirmed. It is found that these compounds have indirect band gaps except for BeTe in NiAs (B8) phase. The results of reflectivity, refractive index and optical dielectric functions of Be compounds are investigated. An agreement is found between our results and those of other theoretical calculations and the experimental data.     

Analysis of structural properties of refractory compounds at high temperature and pressure using a potential model

In this paper we focused on the structural and elastic properties of four transition metal mononitrides (TMNs) (M=Ti, Nb, Hf and Zr) by using realistic three body interaction potential (RTBIP) model, including the role of temperature. These TMN compounds have been found to undergo NaCl (B1) to CsCl (B2) phase transition, at a pressure quite high as compared to other binary systems. We successfully obtained the phase transition pressures and volume changes at different temperatures. In addition, elastic constants of TMNs at different temperatures are discussed. The present theoretical results have been compared with the available experimental data and predictions of LDA theory.     

Pressure dependence of elastic properties of wurtzite ZnO crystal

We present the pressure dependence of elastic properties of the wurtzite phase of ZnO undergoing wurtzite to the rocksalt phase transition. A simple Landau theory is developed to describe the structural phase transition between wurtzite to rocksalt phases observed in ZnO. We have defined the necessary order parameter of the wurtzite to the rocksalt phase transition. We present a detailed analysis of the pressure dependence of the elastic and shear constants of the wurtzite phase of ZnO. The theoretical predictions are in the line with experimental results.