Ab-initio calculations of low-lying excited states of water clusters (H2O)n n = 2-6

摘要

Abstract: In recent years there has been a great deal of interest in excited states of the water molecule with a number of experimental and theoretical studies reported. The umber of spectroscopic studies of complexes involving hydrogen bonding has greatly increased. However, most of this research has involved studies of the IR and Raman vibrational spectra of the molecule hydrogen bond formation strongly perturbs the vibrational transitions, but the changes in the electronic spectrum can also be observed. The interaction between water molecules is dominated by hydrogen bonding and the level of the ab initio theory is used because it accurately reproduces the major components of the interaction energy. Ab initio studies of cyclic water clusters (H$-2$/O)$-n$/, n equals 2 minus 6 and analysis of many-body interactions for ground states of these clusters has been done. The magnitudes of the two-through six-body energy terms and their contribution to the interaction energy of small ring water clusters has been computed at the Hartree-Fock (HF) and second-through fourth-order many-body perturbation (MP2, MP4) levels of theory. In this paper, we investigated the lowest S$-1$/ excited electronic states of the cyclic water clusters (H$-2$/O)$-n$/, n equals 2 minus 6 from the point of changes in the absorption spectra for many-body interactions and examined their trends as the cluster grew. !6