A charge-conserving approximation——method for ab initio calculations

A new method is presented for approximate ab initio calculations in quantum chemistry.It is called CCAM (charge conserving approximation method). The calculation method does notinclude the use of empirical parameters. We use Slater type orbitals as basis set, replacing STO’sby STO-2G functions to evaluate three- and four-center integrals and making the STO-2G two-orbital charge distributions have the same total charge as STO. The results are presented for testcalculations on five molecules. In view of these results, CCAM is better than ab initio calculationsover STO-6G in the results on total energies, kinetic energies and occupied orbital energies. In atomicpopulations, dipole moments and unoccupied orbital energies, CCAM is also satisfactory. Weestimate that CCAM would be as fast as ab initio calculations over STO-2G in evaluating molecularintegrals.