Anharmonic Vibrational Spectra of Hydrogen Bonded Clusters

We report anharmonic vibrational spectra for a variety of hydrogen bonded clusters such as (H$_{2}$O)$_{n}$ and (HF)$_{n}$, $n$=1-5. We investigate the convergence of the hydrogen bonded frequencies with basis set and level of electron correlation and compare with the available experimental data. For this purpose we employ the correlation-consistent basis sets up to quintuple zeta (5z) quality and compute the spectra at the second order M{\o}ller-Plesset (MP2) and Coupled Cluster plus Single and Double with perturbative estimate of Triple excitations [CCSD(T)]. The correlation between the calculated elongations in the hydrogen bonding stretches and the corresponding computed/observed vibrational frequencies suggest an extension of Badger's rule for these hydrogen bonded systems.