基于PBEsol研究高压下HgS同质多相体的结构、弹性以及相变过程

First-principles calculations on structure,elasticity,phase transition of HgS polymorphs with PBEsol under pressure

弹性常数是矿物最重要的物性参数之一,它能为矿物结构的稳定性研究提供很有价值的信息,了解弹性性质与压力之间的关系是认识地球内部动力学过程及性质的基础.本文采用密度泛函理论中的PBEsol泛函对HgS同质异象体高压下的结构、弹性性质（弹性常数、零压下的体积模量及其一阶偏导）进行了研究,分析了HgS的弹性模量和焓随压强的变化情况,并据此得到相变压强.研究表明,β-HgS在约2.22.5 GPa时相变为α-HgS,随着压强进一步增加,α-HgS大概在1221 GPa逐渐从辰砂结构转变为岩盐结构.通过与前人的研究结果对比发现,采用PBEsol得到的HgS晶格参数与实验值更接近,优于前人基于PBE计算的结果,但是本文基于PBEsol和前人基于PBE计算的弹性常数Cij,体积模量和焓与实验都存在不同程度的偏差,并且这两种泛函计算的结果之间也存在差异,这说明在实际应用中,对无法通过实验获得的高压弹性性质,最好选择不同泛函理论计算弹性常数Cij、体积模量和焓并慎重分析.

A modified Perdew-Burke-Ernzerh designed specifically for solids（ PBEsol） has been used to study the phase transition of HgS polymorphs, and the structures, elastic properties of HgS polymorphs such as elastic constants,zero-pressure bulk modulus and its first-order pressure derivative B’ under high pressure（ 0 30GPa） are calculated,then the pressure of phase transition of HgS polymorphs is given based on the elastic modulus and formation enthalpies of HgS. Our research shows that β-HgS undergoes a phase transition to α-HgS at about 2. 2 2. 5 GPa,and with increase of pressure a phase transition from cinnabar structure to rocksalt structure of α-HgS occurs at 12 21 GPa. Compared with the previous studies, the structural parameters obtained using PBEsol are closer to the experimental results than those calculated by previous researchers using PBE,but there exist some differences in the elastic constants（Cij）,bulk modulus（ B） and enthalpy（ H） of HgS between the PBEsol results and the experiments.Though PBEsol reaches a high accuracy for bulk properties（ lattice constant and bulk modulus）,it seems the functions are not suitable for calculating the elastic constants（Cij） of HgS polymorphs.