BENCHMARK STUDIES ON THE PERFORMANCE OF DFT FUNCTIONAL FOR THE ANALISYS OF UNSTABLE ANIONS

JOSÉ LUIS BORIONI ; MARCELO PUIATTI; ADRIANA B. PIERINI

Congreso; 12th CLAFQO; 2013

Over the past 20 years, density functional theory (DFT) has become a much used tool in most branches of chemistry. The study of organic anions has been a challenging task for DFT methods [1] especially in the cases were the anion is unstable or is less stable tan the neutral molecule. These compounds hence have negative electron affinities (EA). In some of the cases (especially increasing the size of basis set) unbound anions are obtained with the extra electron aligned against the dipole of the molecule in an artificial orbital in disagree with the experimental observations. The quality of the DFT results for the study of organic anions with negative EA could be motive of discussion, [2]but we proved that DFT could be appropriate for the study of anions and/or radical anions of organic compounds.[3]

In this work a set of 52 molecules, with negative experimental EAs, with different functional groups was employed as test set for the evaluation of over 25 DFT functionals. Different functionals were employed: pure and hybrids, those with long-range corrections i.e. LC-BLYP, with the dispersion corrections proposed by Grimme i.e. B3LYP-D, the new generation of double hybrid functionals such us B2-PLYP or the mPW2PLYP.

The tendency of giving unbound (non valence) or valence anions and the mean absolute deviation between the experimental and the theoretical EA were evaluated. The best results were obtained with the family of B3LYP functionals, and with B3PW91, PBE0 and M06.

1 - J. Simons, J. Phys. Chem. A, 2008, 112, 6401-6511.

2 - F. Jensen, J. Chem. Theory Comp. 2010, 6, 2726-2735.
3 - M. Puiatti, D. M. A. Vera, A. B. Pierini, Phys. Chem. Chem. Phys., 2009, 19, 8957-89-64.