高压下NaBH₄和NaBH₆的电子能带和声子结构的第一性原理计算研究

First-Principles Calculation on Electronic Band Structure and Phonon Structure for NaBH₄ and NaBH₆ at High Pressures

本文采用基于密度泛函理论的第一性原理计算方法和基于进化算法的晶体结构搜索,研究了配位型储氢材料NaBH4和NaBH6在高压下的结构相变,讨论了高压稳定相的电子能带结构和晶格动力学性质。高压下的NaBH4表现出绝缘特征,其带隙约为5 eV,与金刚石的带隙宽度接近,为超宽带隙(UWBG)材料。随着H比例的提高,高压下的NaBH6显示出金属性,表明高压下的NaBHn材料可通过H含量来调制绝缘-金属转变。声子谱的计算还表明,该系列材料具有高达约1000 cm−1 (约30 THz)的声子带隙,可作为潜在的声子晶体材料用于调制太赫兹频段弹性波的传播。

First-principles calculation method based on density functional theory and crystal structure search based on evolutionary algorithm was used to study the structural phase transition of hydrogen storage materials NaBH4 and NaBH6 under high pressures. We discussed the electronic energy of the stable phase, band structure and lattice dynamics properties. NaBH4 shows insulation characteristics, and its band gap is about 5 eV, which is close to the band gap width of diamond, and is an ultra-wide band gap (UWBG) material. With the increase of H ratio, NaBH6 shows metallicity, indicating that NaBHn material can be modulated by the H content to realize the insulator-metal transition. The calculation of the phonon spectrum also shows a phonon band gap of up to about 1000 cm−1 (~30 THz), which can be used as a potential phononic crystal material to modulate the propagation of terahertz elastic waves.