高压下SiO_2的第一性原理计算

基于密度泛函理论(DFT)的第一性原理,采用Hartree-Fork(HF)方法,分别计算了Si O2的α-石英结构、金红石结构以及氯化钙结构的总能量随体积的变化关系。利用Murnaghan状态方程,通过能量和体积拟合,得到了3种结构的体变模量及其对压强的一阶导数。计算结果表明,随着压强的增加,Si O2会从α-石英结构转变为金红石结构,与实验结果和其它理论结果一致;金红石结构与氯化钙结构之间不存在相变,可以共存。此外,对具有α-石英结构的Si O2的晶格常数、电子态密度和带隙随压强的变化关系进行了计算和分析,结果表明:加压作用下,能带向高能方向移动,Si─O键缩短,电子数转移增加,带隙展宽,电荷发生重新分布。

First Principles Calculation of SiO2 at High Pressures

Total energy of SiO₂ as a function of unit cell volume has been calculated for α-quartz, rutile and CaCl₂ structures using the density function theory (DFT) and Hartree-Fork (HF) method. According to the Murnaghan's equation of state, the bulk modulus B₀ and B′=dB/dp for these three structures have been obtained. The calculated results are all in good agreement with experimental and other theoretical data available in the literature, which indicate that SiO₂ will transform from α-quartz structure to CaCl₂ structure as pressure increasing, and there is no phase transition between rutile structure and CaCl₂ structure, namely they can coexist. By analyzing the changes of the lattice parameters, the electronic density of states, and the band gap under pressure, it is found that in α-quartz SiO₂ the energy band width and charge transfer increase with increasing pressure. Moreover, the Si─O bond length is shortened and the electric charges are redistributed.