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A simplified method for molecular correlation energy calculations by separation into internal and non-internal parts. Application to multiconfigurational zeroth-order wavefunctions

par Liévin, Jacques ;Breulet, Jacques ;Clercq, Philippe;Metz, Jean-Yves
Référence Theoretica chimica acta, 61, 6, page (513-537)
Publication Publié, 1982-11

Article révisé par les pairs

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Résumé :

A simplified method of determining the molecular correlation energy by two separate calculations, one for the internal and one for the non-internal correlation energies, is extended to multiconfigurational zeroth-order wavefunctions. This extension offers the possibility of deriving correlated potential energy curves or surfaces for processes involving configurational changes. The internal correlation energy is shown to be correctly determined by an MC/CI procedure combining the use of minimal and extended basis sets. An original semi-empirical "atoms-in-molecules" method based on the L.C.A.O. expansion of the molecular wavefunction is proposed for the non-internal correlation energy calculations. This method is shown to be able to overcome some of the shortcomings of a previous populations analysis approach. Test calculations concern potential curve parameters (De, Te, Re, We) of the ground and some excited states of the NH, C2, HCN and CN molecules. The results are found to be in good agreement with corresponding experimental and large CI results. © 1982 Springer-Verlag.