Dielectric relaxation in dipolar fluids . Generalized mode approach

The concept of generalized collective modes, recently proposed for the investigation of simple fluids, is now applied to describe processes of di-electric relaxation in dipolar systems. The approach presented here is an extension of the dipole-density formalism to arbitrary numbers of dynami-cal variables and values of wavelengths. Generalized dipolar mode spectra of a Stockmayer fluid are evaluated over a wide scale of wavelengths up to the five-variable approximation. The wavevector-and frequency-dependent dielectric permittivity and dipole-moment time autocorrelation functions are calculated on the basis of analytical expressions using the dipolar modes. The obtained results are compared with those achieved in lower-order approximations and with molecular dynamics data. It is shown that the five-variable description quantitatively reproduces the entire frequency dependence of the dielectric constant at arbitrary wavenumbers.