  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.
