CaX(X=S, Se, Te)带隙的GW近似修正（英文）

采用基于第一性原理下的局域密度近似(LDA)方法对岩石矿物结构Ca硫族化合物CaX(X=S, Se, Te)的晶格常数和电子结构进行了研究.研究结果表明,使用LDA方法得到的晶格常数与实验值符合得很好,但带隙值却远低于实验值.为了获得可靠的带隙值,使用了GW(G格林函数, W库伦屏蔽相互作用)近似方法对Ca硫族化合物的带隙进行修正.利用GW近似方法计算CaS和CaSe的带隙值比利用LDA计算的带隙值高,并且与实验值相吻合.同时也预测了CaTe的带隙值,尽管没有实验值作为参考,但GW近似计算的结果应该是合适的值.

ZnX:Co^(2+)(X=S,Se,Te)中配体对g因子贡献规律的研究

采用双自旋 轨道耦合参数模型和半经验的分子轨道法研究了Co2+离子在Ⅱ Ⅵ半磁半导体ZnX(X=S,Se,Te)中的EPRg因子.结果表明,配体Se和Te对Co2+的g因子有不可忽略的贡献,并且,配体S、Se和Te对相同中心金属Co2+的络离子的EPRg因子的贡献随配体的原子序数变大而依次增加.

Bandgap engineering to tune the optical properties of Be_xMg_(1-x)X(X=S, Se, Te) alloys

Structural, electronic, and optical properties of alloys BexMgl-xX （X = S, Se, Te） in the assortment 0 〈 x 〈 1 were theoretically reported for the first time in zinc-blende （ZB） phase. The calculations were carried out by using full-potential linearized augmented plane wave plus local orbitals （FP-LAPW＋lo） formalism contained by the framework of density functional theory （DFT）. Wu--Cohen （WC） generalized gradient approximation （GGA）, based on optimization energy, has been applied to calculate these theoretical results. In addition, we used Becke and Johnson （mBJ-GGA） potential, modified form of GGA functional, to calculate electronic structural properties up to a high precision degree. The alloys were composed with the concentrations x = 0.25, 0.5, and 0.75 in pursuance of ＇special quasi-random structures＇ （SQS） approach of Zunger for the restoration of disorder around the observed site of alloys in the first few shells. The structural parameters have been predicted by minimizing the total energy in correspondence of unit cell volume. Our alloys established direct band gap at different concentrations that make their importance in optically active materials. Furthermore, density of states was discussed in terms of the contribution of Be and Mg s and chalcogen （S, Se, and Te） s and p states and observed charge density helped us to investigate the bonding nature. By taking into consideration of immense importance in optoelectronics of these materials, the complex dielectric function was calculated for incident photon energy in the range 0--15 eV.

Pressure-induced phase transitions in the ZrXY(X=Si,Ge,Sn;Y=S,Se,Te)family compounds

Pressure is an effective and clean way to modify the electronic structures of materials,cause structural phase transitions and even induce the emergence of superconductivity.Here,we predicted several new phases of the Zr XY family at high pressures using the crystal structures search method together with first-principle calculations.In particular,the Zr Ge S compound undergoes an isosymmetric phase transition from P4/nmm-I to P4/nmm-II at approximately 82 GPa.Electronic band structures show that all the high-pressure phases are metallic.Among these new structures,P4/nmm-II Zr Ge S and P4/mmm Zr Ge Se can be quenched to ambient pressure with superconducting critical temperatures of approximately 8.1 K and 8.0 K,respectively.Our study provides a way to tune the structure,electronic properties,and superconducting behavior of topological materials through pressure.

The Structural,Dielectric,Lattice Dynamical and Thermodynamic Properties of Zinc-Blende CdX(X=S,Se,Te) from First-Principles Analysis

The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the pubfished experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal opticaltransverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX （X= S, Se, Te） are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX （X= S, Se, Te） and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.

N和硫属元素掺杂及共掺杂TiO_2第一性原理计算

采用密度泛函理论(DFT)计算了N、S、Se和Te掺杂及共掺杂金红石TiO2的电子结构。针对DFT方法存在对过渡金属氧化物带隙能的计算结果与实际值严重偏离的缺陷,采用DFT+U(Hubbard系数)方法对掺杂体系的电子结构进行了计算。优化结构的结果表明,掺杂造成二氧化钛的体积膨胀和晶格畸变很明显。相比较于其他元素而言,Te更难掺杂进二氧化钛中是由于其大的原子半径和较大的取代能。能带总态密度图和分态密度图的分析表明,Ti 3d和O 2d轨道与N 2p、S 3p、Se 4p和Te 5p强烈地杂化在一起。与S、Se、Te单掺杂后带隙能比较,由计算的结果(S:2.43;Se:2.42;Te:2.46)可以看出,N/S、N/Se和N/Te共掺杂能明显地改善材料的电子结构及带隙。DFT+U计算结果与实验测量结果较好地吻合。