STATIC DIELECTRIC-PROPERTIES OF A MODEL FOR LIQUID DMSO

Molecular dynamics simulations are used to study the wave vector (k) d ependent static dielectric properties of a recently proposed model (H. Liu, F. Muller-Plathe and W. F. van Gunsteren, 1995, J. Amer. chem. S oc., 117, 4363) for liquid dimethyl sulphoxide (DMSO). Room temperatur e results are given for the real-space orientational pair correlations h(110)(r) and h(112)(r), for the k-dependent short- and long-ranged g eneralized Kirkwood g factors, g(K)(S)(k) and g(K)(L)(k), and for the k-dependent transverse and longitudinal components of the dielectric p ermittivity tensor, epsilon(T)(k) and epsilon(L)(k), over wide ranges of k values. These k-dependent quantities have been obtained from the Fourier-Hankel transforms of the projections h(110)(r) and h(112)(r). The function h(110)(r) reveals that the relative orientation between n eighbouring molecules may result from dipolar forces, and that the loc al order of the molecular dipoles is consistent with the results from other studies on DMSO. The system's shape-independent Kirkwood g facto r calculated from the k --> 0 limit of g(K)(S)(k) is 1 . 6, and using this value in the Kirkwood relation yields epsilon(0) = 44 for the sys tem's dielectric constant. The asymptotic behaviour of h(112)(r) obtai ned from an auxiliary simulation on a 2048 molecules system yields sim ilar estimates for epsilon(0). The calculated values for the model's K irkwood g factor and dielectric constant are in very good agreement wi th experimental data at room temperature. In addition, calculations we re made of the contributions to epsilon(T)(k) and epsilon(L)(k) from t he molecular spatial charge distribution under several different appro ximations. These contributions are essential for a correct characteriz ation of the k-dependent dielectric properties of the model at finite values of k.