Density Functional Theory Calculations of the Structures, Binding Energies, and Infrared Spectra of Methanol Clusters

Abstract

Density functional theory (DFT) calculations of the structures, binding energies, vibrational frequencies and infrared intensities of methanol clusters containing two to five molecules have been carried out using the Becke3LYP functional. Thirteen representative H-bonded structures have been studied including cyclic, chain, branched-cyclic and branched-chain hydrogen bond structures. In the methanol trimer, tetramer, and pentamer, the cyclic structure is more stable by 3.5, 8.3, and 3.6 kcal/mol over the next most strongly bound minimum. In the tetramer and pentamer, the second-most stable minimum corresponds to a branched cycle. Chain structures are destabilized from the cyclic minimum by the loss of a hydrogen bond and from a smaller cooperative strengthening of the H-bonds that remain. In all branched structures studied, the formation of the branch H-bond strengthens the “branch-point” methanol's H-bond donation to its neighbor, but weakens its two acceptor H-bonds, leading to largely compensating effe...