A molecular-dynamics simulation of the orientational melting of potassium perchlorate

A constant-pressure molecular-dynamics simulation of the first-order phase transition of potassium perchlorate is presented. The simulation yields the correct structures in both the low-temperature ordered phase and the high-temperature orientationally disordered phase. While experiments show a rather ill-behaved reconstructive transition, the simulation, despite its excellent agreement with known crystallographic data, follows a very straightforward transition process. This suggests that the behaviour of the real sample, which is presumably connected with the large volume increase at the transition, is driven by effects on a non-microscopic scale.