Transverse wavevector dependent and frequency dependent dielectric function, magnetic permittivity and generalized conductivity of interaction site fluids. MD calculations for the TIP4P water

Abstract

It is shown that the dielectric properties of interaction site models of polar fluids can be investigated in computer experiment using not only the charge fluctuations but also correlations corresponding to a current of moving charges. This current can be associated with a generalized dynamical polarization or separated into electric and magnetic components. The first approach deals with the dielectric permittivity related to a generalized conductivity, whereas the second one leads to the functions describing polarization and magnetization fluctuations separately. The last way is only the source to calculate the magnetic susceptibility for a system of interaction sites. The transverse wavevector- and frequency-dependent dielectric functions and magnetic susceptibility are evaluated for the TIP4P water model in a very wide scale of wavelengths and frequencies using molecular dynamics simulations. We demonstrate that the transverse part of the dielectric functions may differ drastically from their longitudinal component. A relationship between the two approaches is discussed and the limiting transition to the static dielectric constant in the infinite-wavelength regime is analyzed. The propagation of transverse electromagnetic waves in the TIP4P water is also considered.