The structures of solid hydrogen under high pressures have been revisited by using first-principles electronic structure calculations. Focusing on the stability, the intramolecular bond strength of hydrogen molecules in solid hydrogen, and the cell volume, we made a comparison study on seven structures including $P21/c\text{−}24$, $C2/c\text{−}24$, $P6122\text{−}36$, $Pc\text{−}48$, $Pca21\text{−}48$, $Cmca\text{−}4$, and $Cmca\text{−}12$ with the recently proposed strongly constrained and appropriately normed (SCAN) functional and three conventional exchange-correlation functionals, namely Perdew-Burke-Ernzerhof (PBE), Becke-Lee-Yang-Parr (BLYP), and van der Waals-density functional (vdW-DF). On one hand, with the SCAN functional the $C2/c$ structure takes the minimum static lattice enthalpies in the pressure range from 150 to 450 GPa, which agrees with the recent synchrotron infrared spectroscopic study and is similar to the result of the BLYP functional. On the other hand, the vibration frequencies of hydrogen molecules calculated by the SCAN functional match well with the experimental characteristic IR and Raman peaks, which indicates that the SCAN functional gives a reasonable estimation of the bond strength or bond length of hydrogen molecules in solid hydrogen, while the BLYP and vdW-DF functionals overestimate the bond strength. All SCAN, PBE, BLYP, and vdW-DF functionals give a good estimation of the unit cell volumes. Thus, the structures optimized with the SCAN functional can be an excellent starting point for advanced works on solid hydrogen.

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固体氢的第一性原理研究：四种交换相关功能之间的比较

固态氢在高压下的结构已经通过第一性原理电子结构计算得到了重新探讨。着眼于稳定性，氢分子在固体氢分子中的分子内键合强度以及细胞体积，我们对以下七个结构进行了比较研究：$P21/C\text{-}24$， $C2/C\text{-}24$， $P6122\text{-}36$， $PC\text{-}48$， $PC\mathrm{一种}21\text{-}48$， $C米C\mathrm{一种}\text{-}4$和 $C米C\mathrm{一种}\text{-}12$以及最近提出的强约束和规范化（SCAN）功能以及三种常规的交换相关功能，即Perdew-Burke-Ernzerhof（PBE），Becke-Lee-Yang-Parr（BLYP）和van der Waals密度功能（ vdW-DF）。一方面，借助SCAN功能$C2/C$该结构在150至450 GPa的压力范围内具有最小的静态晶格焓，这与最近的同步加速器红外光谱研究一致，并且与BLYP功能的结果相似。另一方面，通过SCAN官能团计算出的氢分子的振动频率与实验特征IR和拉曼峰相吻合，这表明SCAN官能团对固体氢中氢分子的键强度或键长给出了合理的估计。 ，而BLYP和vdW-DF功能则高估了粘合强度。所有的SCAN，PBE，BLYP和vdW-DF功能都可以很好地估计晶胞体积。因此，利用SCAN功能进行优化的结构可以成为固体氢高级研究的绝佳起点。