OPTIMIZED GAUSSIAN EXPANSION OF ATOMIC ORBITALS

SIRIRAT HO-AMPAWANWONG

Summary: Property-optimized Gaussian expansions of Slater-type orbitals (STO) were used to calculate the ground state energy and the one-electron molecular properties of the water molecule and the NH₂ species. The effect of simultaneously using a weighting factor and pseudonormalization was studied. The weighting factor was seen to give a definite improvement: in the energy calculation, the weighting factor r^-1 gives satisfac. tory results, i.e. the energy is improved by about 0.7 a.u. (from -72.78278 a.u. to -73.52642 a.u.) compared tq the un weighted expansion with STO-2G for the water molecule (at a bond angle of 105^o). The weighting factor r¹ gives an extremely good result in the dipole moment calculation. For the water molecule with STO-2G it is 0.5633 a.u. while the unweighted filting gives 0.4954 a.u. compared to the STO result of 0.5642 a.u.

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Department of Chemistry. Faculty of Science, Chulalongkorn University. Phya Thai Rd., Bangkok, Thailand.

Received 2 September 1980