DFT calculated THz absorption spectra of water clusters

Abstract

Calculations are presented of vibrational resonance structure at THz frequencies for a 38 molecule cluster of H2O using density functional theory (DFT). This resonance structure is due to coupling of molecular vibrational modes. In particular, the coupling among resonance modes provides a reasonable molecular level interpretation of spectral features associated with THz excitation of molecular clusters. THz excitation is associated with frequencies that are characteristically perturbative to molecular electronic states, in contrast to frequencies that can induce appreciable electronic state transition. Owing to this characteristic of THz excitation, one is able to make a direct association between local oscillations about ground-state minima of molecules comprising a cluster and THz excitation spectra. The DFT software GAUSSIAN was used for the calculations of vibrational resonance structure presented here.