Molecular dynamics simulation of structural phase transitions in RbNO₃ and CsNO₃

Structural phase transitions in RbNO₃ and CsNO₃ are studied by molecular dynamics. The simulations are based on the parameter-free potentials calculated from the Gordon-Kim modified electron gas formalism, extended to ionic molecular crystals. The microscopic mechanism of the structural phase transitions in RbNO₃ and CsNO₃ is revealed. It is found that the phase IV-III transition in RbNO₃ and the phase II-I transition in CsNO₃ are initiated by the in-plane and out-of-plane rotations of the NO₃ ions, and the phase III-II-I transitions in RbNO₃ are due to dilation along a trigonal axis of phase III, giving phase II a rhombohedral structure.