MOLECULAR-DYNAMICS STUDY OF THE PHASE-TRANSITION IN (CH3)(3)NHCL

Molecular dynamics simulation has been performed on the hydrogen bonde d crystal of (CH3)(3)NHCl at ten different temperatures between 200 an d 380 K in the rigid-body approximation. Changes of the unit cell para meters and average molecular orientation and position clearly show tha t a phase transition, from an ordered monoclinic phase to a tetragonal rotator phase, occurs at about 305 K in good agreement with experimen tal results. In the rotator phase, three methyl groups of the molecule distribute around four distinguishable positions keeping away from ch loride ions. This can be interpreted as the mode coupling between rota tion and translation.