Gaussian Basis SCF Calculations for OH−, H2O, NH3, and CH4

Extensive SCF LCAO MO calculations utilizing comparable Gaussian basis sets for OH−, H2O, NH3, and CH4 give SCF energies of −75.377, −76.034, −56.201, and −40.198 a.u., respectively. An ad hominem assumption of an error of 0.03 a.u. due to an incomplete basis set in each calculation leads to estimates of −75.41, −76.06, −56.23, and −40.23 a.u., respectively, for the Hartree—Fock limits, and of −0.39, −0.38, −0.33, and −0.28 a.u., respectively, for the correlation energies of these molecules. Details of the use of linear combinations of Gaussian functions as bases in molecular calculations are presented. The results show that considerable computation time can be saved with little sacrifice in accuracy for well-chosen combinations.