Scaling the Coulomb interaction in calculations of electron spectra of transition metal complexes

A simple technique of scaling two-electron integrals in ab initio calculati ons of the electronically excited states of transition metal complexes is p roposed. This technique uses the fact that one-center two-electron integral s depend linearly on the scaling factor when Slater type functions are subj ected to scaling transformation. This leads to a linear dependence of the d -d transition energy on the "scale" of Coulomb interaction,, which allows o ne to affect the calculation result by varying the Slater exponential. To t est the technique, ab initio configuration interaction and full active spac e calculations of the low excited states of the CrF63-, MnF62-, and VF63- c omplexes are performed For transition elements, a basis of Slater type effe ctive functions chosen front the optical spectra of the atoms and ions of t ransition elements is used. It is shown that in the STO-6G basis with effec tive exponentials, experimental transitions are reproduced with an accuracy of about 2000 cm(-1) even with the use of small active space determined by the orbitals localized on the central atom of the complex.