  We report simulated infrared spectra of deuterated water and ice using
Car-Parrinello molecular dynamics with maximally localized Wannier functions.
Experimental features are accurately reproduced within the harmonic
approximation. By decomposing the lineshapes in terms of intra and
intermolecular dipole correlation functions we find that short-range
intermolecular dynamic charge fluctuations associated to hydrogen bonds are
prominent over the entire spectral range. Our analysis reveals the origin of
several spectral features and identifies network bending modes in the far IR
range.
