Vibrational analysis of glycine zwitterion – an ab initio study

It is known that the ab initio electronic structure calculations on isolated amino acid zwitterions do not reproduce experimental vibrational frequencies and their potential energy distribution(PED), obtained from solution and/or solid phases, because of intramolecular hydrogen bonding. In this paper we show that using Onsager reaction field model with a proper choice of basis set, cavity radius and dielectric constant followed by the scaling of force constants can indeed mimic the features of the experimental results very well for the simplest amino acid glycine zwitterion.