Comparative Tests of Theoretical Procedures for Studying Chemical Reactions

摘要

A simple procedure is described for estimating the effective errors in molecular energies calculated by ab initio methods with respect to use of the latter in studies of chemical reactions. The procedure is illustrated by application to the STO-3G, 3-21G, and 6-31G* models. Parallel results from semiempirical models (MINDO/3, MNDO, AMI) are included for comparison. The STO-3G, 3-21G, and 6-31G* basis sets cover a wide range, from a minimum basis set (STO-3G) to a split basis set with polarization functions (6-31G*). These have been extensively used and the results of calculations for quite a wide range of molecules are listed in a compilation by People et al. Using them, we determined values of and e sub p and e sub p prime for carbon, hydrogen, nitrogen, and oxygen for each of the basis sets indicated above. These are listed in Table II, in atomic units (hartrees), for conformity with published values for the calculated molecular energies. Conversion factors to other units are shown in a footnote to the table.