DFT study of [BH4]− rotation in pressure-driven phase transition of MBH4

The pressure-induced phase transitions of MBH4 (M = Na, K) have been studied using first-principles calculations. The optimized results indicate that their high-pressure phases are space group P42/nmc, which have the same symmetry as the C-substructure of their low-pressure phases. The result of [BH4]− rotational barrier shows that rotational barrier will increase with the increase of external pressure. The rotational energy barrier of KBH4 is larger than that of NaBH4 at same pressure due to larger radius of potassium atom, which can explain why potassium borohydride has a lower phase transition pressure. The theoretical rotation barrier obtained with Tkatchenko-Scheffler correction is higher and is more sensitive to change under different pressures than that without vdW correction.