Computer simulation study of thermodynamic scaling of dynamics of 2Ca(NO3)2 • 3KNO3

Molecular dynamics (MD) simulations of the glass-former 2Ca(NO3)(2) center dot 3KNO(3), CKN, were performed as a function of temperature at pressures 0.1 MPa, 0.5 GPa, 1.0 GPa, and 2.0 GPa. Diffusion coefficient, relaxation time of the intermediate scattering function, and anion reorientational time were obtained as a function of temperature and densitiy rho. These dynamical properties of CKN scale as. rho(gamma)/T with a common value gamma = 1.8 +/- 0.1. The scaling parameter gamma is consistent with the exponent of the repulsive part of an effective intermolecular potential for the repulsion between the atoms at shortest distance in the equilibrium structure of liquid CKN, Ca2+, and oxygen atoms of NO3-. Correlation between potential energy and virial is obeyed for the short-range terms of the potential function, but not for the whole potential including coulombic interactions. Decoupling of diffusion coefficient and reorientational relaxation time from relaxation time take place at a given rho(gamma)/T value, i.e., breakdown of Stokes-Einstein and Debye-Stokes-Einstein equations result from combined thermal and volume effects. The MD results agree with correlations proposed between long-time relaxation and short-time dynamics, ln tau proportional to 1/< u(2)>, where the mean square displacement < u(2)> concerns a time window of 10.0 ps. It has been found that < u(2)> scales as rho(gamma)/T above and below the glass transition temperature, so that thermodynamic scaling of liquid dynamics can be thought as a consequence of theories relating short-and long-time dynamics, and the more fundamental scaling concerns short-time dynamical properties. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3656872]