Theoretical study of disorder-order transition of sodium borohydride

[Display omitted] •Disorder-order phase transition.•van der Waals interactions.•Rotational barriers. The disorder-order phase transition of NaBH4 from the cubic to tetragonal structures has been studied based on density functional theory. The disordered high temperature phase is expressed as a statistical average of three substructures with a hypothesis that each BH4− tetrahedron has a fixed orientation. Our calculations show that the phase transition is mainly induced by synergic rotation of BH4− ion and the energy barrier is sensitive to volume change. We also investigated the role of van der Waals corrections in describing phase transition with DFT-D2 and vdW-DF methods.