Prediction of the Raman spectrum of the aqueous formate anion by a combined density functional theory and self-consistent-reaction-field study

Formate, HCOO-, is a small ion that can be used as a convenient model to re present general carboxylic acids as well as the terminal side chains of glu tamic and aspartic amino acids in biological systems. Several ab initio tec hniques (Hartree-Fock and density functional theory methods) were used to s tudy the formate anion in aqueous solution, where the solvent was treated a s an electrostatic influence by means of a self-consistent-reaction-field ( SCRF) method. The comparison of calculated frequencies with Raman experimen tal data constitutes a good test for the solvation model employed in this w ork. The results showed that the application of a SCRF method not only prod uced smaller errors but also improved the linear correlation between predic ted and experimental values. This latter characteristic enables a more effi cient application of a linear scaling factor, lambda, which corrects the ca lculated frequencies. In fact, the application of lambda to the values calc ulated for the continuum, when compared to those obtained for a vacuum, res ulted in smaller root-mean-square errors of the deviations from the experim ental data.