Optimal Selection of Partial Charge Calculation Method and Equilibrium Molecular Geometry for Rapid Estimation of Enthalpies of Formation from Hartree-Fock Total Energy and Partial Charges

ADRIENN RUZSINSZKY1, CHRISTIAN VAN ALSENOY2, GÁBOR I. CSONKA1

 1	Department of Inorganic Chemistry, Budapest University of Technology and Economics, 
H-1521 Budapest, Hungary
 2	University of Antwerp UIA , Department of Chemistry, Universiteitsplein 1, B-2610 Antwerpen, Belgium

ABSTRACT - The Rapid Estimation of Basis set Error and Correlation Energy from Partial Charges (REBECEP) method [1] is improved further in several ways in the current paper . We introduce the total energies derived from experimental enthalpies of formation instead of G3 energies in the fitting procedure. This increases the precision because the error of the G3 method is eliminated. We test the use of B3LYP/6-31G(d) equilibrium geometries instead of MP2/6-31G(d) geometries. This provides a considerable speed up. We also test the application of stockholder charges in the fitting procedure. New REBECEP parameters were obtained from HF/6-311+G(2d,p) and HF/6-31G(d) energies and atomic charges (natural populatiom analysis, Mulliken, and stockholder). 117 closed-shell neutral molecules from the G2/97 and G3/99 database [2] composed of H, C, N, O, and F atoms were selected for the present study. While the correlation between various charges is reasonable for H, C, and N atoms, there is a rather poor correlation between natural population analysis and stockholder charges for O and F atoms. The best REBECEP results were obtained using the HF/6-31G(d) natural population analysis charges. The root-mean-square deviation from the experimental enthalpies of formation for the selected 117 molecules is 2.16 kcal/mol (the average absolute deviation is 1.65 kcal/mol). This is a considerable improvement compared to our previous results (root-mean-square deviation: 2.92 kcal/mol, average absolute deviation: 2.27 kcal/mol). The results are compared to Gaussian-3, and B3LYP/6-311+G(3df,2p) enthalpies of formation (the corresponding average absolute deviations are 0.94, 7.09 kcal/mol, respectively). The REBECEP method performs considerably better for the 117 molecules with a moderate 6-31G(d) basis set than the B3LYP method with large 6-311+G(3df,2p) basis set.

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References

1 	S. Kristyán, A. Ruzsinszky, G.I. Csonka, Theoret. Chem. Acc. 106, 404 and 319 (2001).
3	L. A. Curtiss, P. C. Redfern, K. Raghavachari, and J. A. Pople, J.Chem. Phys. 109, 42 (1998). http://chemistry.anl.gov/compmat/g2-97.htm

Keywords - Enthalpies of formation, correlation energy, basis set error, partial charges.
Section 1 : ESAM