Implicit Zero-Point Vibration Energy and Thermal Corrections in Rapid Estimation of Enthalpies of Formation from Hartree−Fock Total Energy and Partial Charges

Abstract

The rapid estimation of basis set error and correlation energy from partial charges (REBECEP) method is improved in a way that makes superfluous the explicit zero-point energy and thermal correction calculations. This saves considerable computational effort and increases the computational efficiency of the method. The new REBECZTEP (zero-point energy and thermal correction included) parameters provide an energy that can be used to calculate an enthalpy of formation using atomic enthalpies and energies without any further correction. An intermediate level where only the zero-point energy is included in the parameters, REBECZEP parameters, is also studied. The performance of the new parameter set that corrects the HF−SCF energy using atomic partial charges was studied for the 6-31G(d) and 6-311+G(2d,p) basis sets, for Mulliken, natural population, and stockholder charges. A total of 117 closed-shell neutral molecules with correctly measured experimental enthalpies of formation from the G2/97 and G3/99 database composed of H, C, N, O, and F atoms were selected for the test. The best REBECZTEP results were obtained using the HF/6-311+G(2d,p) natural population analysis charges. The average absolute deviation from the experimental enthalpies of formation for 115 molecules is 1.48 kcal/mol. This deviation was decreased to 1.22 kcal/mol on a reduced set of 110 molecules. This compares favorably to our previous best REBECEP results on the same test set of 117 molecules (average absolute deviation: 1.65 kcal/mol). These results also compare favorably to Gaussian-3 and B3LYP/6-311+G(3df,2p) enthalpies of formation (for 51 large molecules the corresponding average absolute deviations are 0.94 and 7.09 kcal/mol, respectively). The considerably faster REBECZTEP 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.