高压下H3S-MH4(M = C, Si, Ge, Sn)的非谐量子效应及其超导电性的理论研究

甲烷在高压下发生分解，而其它第IVA族氢化物出现压致金属化现象，并呈现良好的超导特性，前期研究表明，H3S已经接近室温超导体，而且通过掺杂必然会大幅提升超导特性。因此本项目选择新型化合物H3S-MH4(M=C,Si,Ge,Sn)为研究对象，以期获取新型超导材料。本项目采用第一性原理方法结合结构搜索技术，寻找不同压力条件下体系中能量最低的晶体结构。利用线性响应理论获得其声子谱和声子态密度，基于随机自洽简谐近似（SSCHA）算法对晶体能量及动力学矩阵做出修正后，从热力学、晶格动力学多角度判断各结构在高压下的稳定性。研究这些结构在高压下的能带结构和态密度，通过费米面处的能带交叠判断是否转变为金属相；计算金属相的电声子相互作用参数；通过基于BCS理论的McMillan修正公式计算超导转变温度；该项目的研究可以为富氢化合物超导转变机制的揭示与新型超导材料的研发和利用提供理论依据和支持。

Under high pressure, many IVA group hydrides are metallic and superconducting, such as germane, silane, Stannane etc. However, methane is not metallic and high-pressure induced decomposition appears under high pressure. It has been shown that H3S is closed to room temperature superconductor in earlier studies. And the superconducting properties will inevitably be greatly improved through doping. Therefore, the new compound H3S-MH4(M = C, Si, Ge, Sn) have been selected in this project in order to obtain new kinds of superconductor. The crystal structure searching technology based on the random and evolutionary algorithms combined with the first principle methods are used to find the lowest energy crystal structure. With the crystal structures and their dynamical matrices being modified by the stochastic self-consistent harmonic approximation method(SSCHA), the phonon spectra and phonon density of states of the candidate structures are calculated by PWSCF base on the linear response theory. The structural stability and stable pressure range of candidate structures are determined by the thermodynamics and lattice dynamics. We will also study the band structure and the density of states at high pressures. The metallicity of the candidate structures is determined by the energy band overlapping near the Fermi level. The phonon spectrum of metallic phases and electron-phonon interaction are calculated by using linear response theory. The superconducting critical temperature Tc can be calculated by using the modified McMillan formula based on BCS theory. This research can provide theoretical basis and supporting for the discovery of the superconducting transformation mechanism of hydrogen-rich compounds and the development and utilization of new superconductors.