Molecular-dynamic study of the molecular glass model forRb1−x(ND4)xD2PO4

A two-dimensional model with four protons and two effective rubidium or ammonium particles per unit cell has been studied by the molecular-dynamic method. The symmetry properties of the phase transitions of ${\mathrm{RbD}}_2$ ${\mathrm{PO}}_4$ and ${\mathrm{ND}}_4$ ${\mathrm{D}}_2$ ${\mathrm{PO}}_4$ are used as input data for the simulation. The mixed system shows a glassy behavior. The freezing temperature $T_f$ has been found by studying the glass order parameter ${\eta }_{\tau }$. $T sub f— depends on the time over which ${\eta }_{\tau }$ has been averaged. The calculations showed that below $T_f$ the mixed system can go to many local minima which differ by displacement patterns. With the use of the multiple molecular-dynamic method with time averages and configurational averages over local minima, the diffuse scattering function and the dynamical structure factor have been calculated. Diffuse streaks along the high-symmetry axes of the crystal have been found. The width of the diffuse streak and of the quasielastic scattering exhibit a change of slope as a function of temperature, in agreement with the neutron-experimental observations.