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