Molecular dynamics simulations of orientational relaxation in dipolar lattice: lack of diffusive decay for second and higher rank correlation functions

Abstract

Extensive molecular dynamics simulations have been carried out to calculate the orientational correlation functions C_l(t), C_l(t) = [4 π/(2l + 1)]Σ_m=-l^l [Y*_lm(Ω(0)) Y_lm(Ω(t))] (where Y_lm(Ω) are the spherical harmonics) of point dipoles in a cubic lattice. The decay of C₁(t) is found to be strikingly different from higher l-correlation functions-the latter do not exhibit diffusive dynamics even in the long time. Both the cumulant expansion expression of Lynden-Bell and the conventional memory function equation provide very good description of the C₁(t) in the short time but fail to reproduce the observed slow, long time decay of C₁(t).