APPLICATIONS OF THE ADIABATIC CONNECTION METHOD TO CONFORMATIONAL EQUILIBRIA AND REACTIONS INVOLVING FORMIC-ACID

Density Functional Theory (DFT) was used in this paper to study the conformational equilibria, vibrational spectra and reactions involving formic acid. The purpose of this study is two-fold: to resolve experimental discrepancies and to compare DFT results with high level ab initio results. First, we investigated structures and vibrational properties of trans and cis conformers of formic acid. We examined two unimolecular dissociation reactions and one internal rearrangement reaction. Local (LSD), non-local (NLSD) and the latest adiabatic connection (ACM) density functional approaches have been used. The barrier heights to the above mentioned reactions including zero point vibrational energy corrections were calculated and are in agreement with high level CCSDT-1 ab initio and the latest experimental results. In general, the ACM functional provides better geometries and reaction energetics than the BP86 non-local functional studied.