金红石结构TiO2结构和热力学性质的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法以及准谐德拜模型研究了金红石TiO2的结构和热力学性质。常温常压下所计算的晶格常数、体弹模量及其对压强的一阶导数与实验值和其他理论计算结果相符的较好。另外,我们还计算了体弹模量、热膨胀系数、热容与温度和压强的关系。     

C掺杂金红石相TiO2的电子结构和光学性质的第一性原理研究

运用第一性原理的局域密度近似+U(0 ≤U≤9 eV)方法研究了本征金红石相TiO₂在不同U值(对Ti-3d电子)下的禁带宽度、晶体结构以及不同比例C元素掺杂的金红石相TiO₂的电子结构和光学性质, 研究表明, TiO₂的禁带宽度和晶格常数随着U值的增加而增大. 综合考虑取U=3 eV并对其计算结果进行修正. 对于掺杂体系, 发现C 元素的掺杂在金红石相TiO₂中引入杂质能级, 杂质能级主要由O-2p轨道和C-2p轨道耦合形成, 杂质能级的引入可以增加TiO₂对可见光的响应, 从而使TiO₂的吸收范围增大. C原子掺杂最佳比例为8.3%, 此时光学吸收边的红移程度最明显, 可增大光吸收效率, 从而提高了TiO₂光催化效率.     

NbSi2奇异高压相及其热力学性质的第一性原理研究

采用基于粒子群优化算法的结构预测程序CALYPSO, 并结合第一性原理的VASP程序, 在175 GPa发现NbSi₂的奇异立方高压相. 在此结构中, Nb原子形成金刚石结构, 而Si原子则形成正四面体镶嵌在金刚石结构中. 声子谱计算结果表明该结构是动力学稳定的. 电子结构分析表明, 六角相和立方相NbSi₂均为金属, 对金属性贡献较大的是Nb原子, 而且Nb和Si原子之间存在明显的p-d杂化现象, 电荷更多地聚集在Si四面体中. 利用“应力应变”方法, 计算了NbSi₂的弹性常数, 分析了其体积模量、剪切模量、杨氏模量和德拜温度等热动力学性质随压力的变化并进行了详细的讨论. 根据剪切模量和体积模量的比值分析了NbSi₂两种相结构的脆性和延展性, 发现压力会导致六角相NbSi₂的延展性增加, 但对立方相结构的延展性影响较小; 采用经验算法计算了NbSi₂两种相结构硬度变化情况, 结合这一比值进行了详细的分析. 弹性各向异性计算结果表明, 随着压力增加, 六角结构的各向异性增强, 而立方结构的各向异性减小.     

N-S共掺杂金红石相TiO2电子结构与光学性质的第一性原理研究

采用基于第一性原理的平面波超软赝势方法研究N和S单掺杂以及N和S共掺杂金红石相TiO2的能带结构,态密度和光学性质.结果表明:N掺杂导致禁带宽度减小为1.43 eV,并且在价带上方形成了一条杂质能带;S掺杂导致费米能级上移靠近导带,直接带隙减小为0.32 eV;N和S共掺杂导致能带结构中出现了两条杂质能带,靠近导带的一条杂质能级距离导带底约0.35 eV,靠近价带的一条杂质能级距离价带顶约0.85 eV,杂质能级主要由N原子的2p轨道和S原子的3p轨道组成.N和S掺杂后不但使TiO2的吸收带产生红移,而且在可见光区具有较大的吸收系数,光催化活性增强.     

ZrV2结构、弹性和热力学性质的第一性原理计算

采用基于密度泛函理论的第一性原理平面波赝势方法研究ZrV₂的晶体结构和弹性,利用准谐Debye模型计算在不同温度(T=0~1200 K)和不同压强(P=0~20 GPa)下ZrV₂的热力学性质,包括弹性模量与压强,热熔与温度,以及热膨胀系数与温度和压力的关系.结果表明:计算的ZrV₂晶格常数与实验值符合较好,晶体材料的弹性常数随着压力增加而增加;在一定温度下,相对体积、热熔随着压强的增加而减小,德拜温度、弹性模量随着压强的增加而增加,且高压下温度对ZrV₂热膨胀系数的影响小于压强的影响.     

PtN2的结构和力学性质的第一性原理计算

采用平面波赝势密度泛函理论方法计算了PtN₂的坐标、平衡态的晶格常数、体弹模量、剪切模量和弹性常数,计算结果与已有的实验值和理论值符合较好.通过能量与体积曲线,可知ST_AA结构比黄铁矿结构具有更低的能量.根据计算结果和Pugh提出的经验判据,PtN₂是易脆的硬物质,随着压强增加PtN₂的脆性逐渐过渡到延性.两种结构的能带结构和态密度表明了黄铁矿结构的PtN₂是半导体而ST_AA 关键词： 2')" href="#">PtN₂ 第一性原理 力学性质     

高氧空位浓度对金红石TiO2导电性能影响的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法研究了 纯的和不同高氧空位浓度金红石型TiO_2-x (x=0, 0.083, 0.125, 0.167, 0.25)超胞的能带结构分布、态密度分布.同时, 采用局域密度近似+U方法调准了带隙.结果表明, 高氧空位浓度越高, 金红石型TiO₂的最小带隙越变窄、电子有效质量越减小, 自由电子浓度越高, 电子迁移率越低、电导率越低.计算结果与实验结果的变化趋势相符合. 关键词： 高氧空位 2')" href="#">金红石型TiO₂ 电导率 第一性原理     

ZrH2结构与热力学性质

基于密度泛函理论,采用全势线性缀加平面波加局域轨道方法和广义梯度近似研究了ZrH2的结构与弹性性质。结果表明：在基态条件下,ZrH2的晶格常数计算值与实验值及其它理论值相当吻合。在考虑声子作用的前提下,采用准谐德拜模型成功获得了不同条件下(0~50 GPa, 0~1 300 K) ZrH2的热容、热膨胀系数和德拜温度等热力学性质。结果表明：定压热容预测值随温度升高而增大,并逐渐接近佩蒂特-杜隆极限;随压强增加,德拜温度呈增加趋势;随温度增加,德拜温度呈减小趋势;在压强一定的条件下,热膨胀系数随温度的升高而增大,且在高温高压条件下,热膨胀系数的增加趋势变缓。     

共掺杂金红石TiO2的电子结构和红外光谱研究

本文对大别山双河、碧溪岭地区硬玉石英岩中的金红石进行了Fourier变换红外光谱(FTIR)分析, 结果显示所有金红石颗粒分别在3280 cm^-1和3295 cm^-1 出现强的吸收峰. 基于前人提出H在金红石结构中以孔道中心(CC)和八面体共边(BOE)方式存在的两种模型, 本文采用第一性原理计算方法研究了掺杂(Al, H)和(Fe, H)时金红石相TiO₂的晶体结构和电子结构. 根据O—H键的振动频率和O—H…O键中O—O之间距离的经验关 关键词： 2')" href="#">金红石相TiO₂ 孔道中心 电子结构 第一性原理     

Mg2Sn电子结构及热力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了Mg₂Sn基态的电子结构、弹性常数和热力学性质.计算结果表明Mg₂Sn的禁带宽度为0.1198eV.运用线性响应方法确定了声子色散关系和态密度,得出Mg₂Sn的热力学性质如等容比热和德拜温度.计算Mg₂Sn的热导率并与实验数据相比较. 关键词： 第一性原理 电子结构 弹性常数 热力学性质     

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.     

Structural and Thermodynamic Properties of TiAl intermetallics under High Pressure

The structural and thermodynamic properties of TiAl intermetallics under high pressure have been investigated by ab initio plane-wave pseudopotential density functional theory method.It is found that the ratio of lattice parameter c to a keeps almost constant with a value of 1.02 under the pressure from 0 to 20 GPa,which agrees well with the experimental results.With the pressure increasing from 20 to 45 GPa the values of c/a decrease almost linearly from 1.02 to 0.99.These calculated results indicate under low pressure the variation rate for a-axis is almost the same to that for c-axis,but under higher pressure the variation for a-axis is smaller than along c-axis.Through the quasi-harmonic Debye model,the equation of state(EOS) of TiAl intermetallics,as well as the thermal expansion and heat capacity at various pressures and temperatures are also studied.     

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 Poisson＇s ratio （v）, the Griuneisen parameter （γ）, the Debye temperature θD on pressure and temperature are also successfully 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 c_ij 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 Poisson's ratio (υ), the Grüneisen parameter (γ), the Debye temperature Θ_D on pressure and temperature are also successfully obtained.     

Structural and Thermodynamic Properties of Wurtzitic Boron Nitride from First-Principle Calculations

Using ab initio plane-wave pseudopotential density functional theory method, we have studied the structural and thermodynamic properties of the wurtzite boron nitride （w-BN）. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependencies of the normalized lattice parameters a/ao and c/co, the axial ratio c/a, and the normalized primitive cell volume V/Vo on pressure P and temperature T are investigated. Furthermore, the Debye temperature θ, the variation of thermal expansion α, as well as the heat capacity Cv as functions of P and T are studied systematically.     

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-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 Grüneisen 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/V₀ and pressure, the elastic constants underhigh 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 α with pressure P and temperature T are obtained systematically in the ranges of 0-870 GPa and 0-1600 K.