Simultaneous optimization of GTF exponents and their centers with fully variational treatment of Hartree-Fock molecular orbital calculation

We have proposed the fully variational molecular orbital (FVMO) method by w hich all parameters in the molecular orbitals are optimized under the varia tional principle. According to the fully variational treatment within the H artree-Fock approximation, exponents and centers in the Gaussian-type funct ion (GTF) basis set are determined simultaneously, as well as the linear co mbination of atomic orbital (LCAO) coefficients. The FVMO method gives the lowest energy under the variational principle, improves the flexibility of wave function drastically, and raises the ab initio (nonempirical) feature. In the calculation of the adiabatic potential for HeH+, the electron movem ent for dissociation limitation is smoothly expressed due to full optimizat ion of GTF centers and exponents under a condition that satisfies the Hellm ann-Feynman and virial theorems. Properties such as dipole and polarizabili ty of the hydrogen and helium atoms and the LiH molecule are in good agreem ent with the numerical Hartree-Fock values, even if only s type GTFs are us ed. We have also applied the FVMO method to H2O and CH4 molecules. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 197-510, 1999.