Correlated gaussian wavefunctions

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Abstract
Variationally optimized correlated wavefunctions for H2 and H3 + at equilibrium geometry are presented. The expansion functions are Φ and {Gk + Φ}, where Φ is a self-consistent field determinant and {Gk + Φ} is a function which is approximately strongly orthogonal to Φ. Gk (r1, r2) are correlated gaussians of the form exp (-ar 1 A 2 - br 2 B 2 - cr 12 2), and {Gk + Φ} is constructed using a strong orthogonality projection operator. Using only three of these functions, variational energies of -1·17001 a.u. for H2 and -1·34058 a.u. for H3 + are obtained. The accuracy of these results suggests that the method ought to be considered for small molecules.