A geminal model chemistry

Abstract

We modify the existing model of the antisymmetrized product of strongly orthogonal geminals to define a size consistent variational theory free from any adjustable parameters apart from the usual choice of a basis set. The new theory is only slightly more computationally expensive than Hartree–Fock, gives an exact solution for an ensemble of noninteracting singlet two electron systems, and is applicable to open- and closed-shell systems. We use it to calculate equilibrium geometries, vibrational frequencies, and dipole moments of diatomic molecules from G2/97 database. We find excellent agreement with experimental values for covalently bound molecules, and overstretched bonds of molecules formed by atoms with extreme electronegativity.