Environmental considerations in ab initio calculations of electronic states of PtCl4-2 complexes

Many quantum chemical methods used for large complexes are based on a limited treatment of electrons due to the computational demand dictated by the number of electrons that must be considered explicitly, especially when considering chemical environment. Such treatments can fail to correlate accurately with electronic spectra. Ab initio electronic structure theory using the spin-orbit configuration interaction method is applied in a study of spectral transitions in PtCl42- including environmental effects. In this method electronic wave functions are eigenfunctions of the total angular momentum operator belonging to one of the symmetry types of the molecular double group. PtCl42- is investigated as a charged gas phase complex, a point-charge-neutralized complex, and a pseudopotential-neutralized complex. It is seen that the use of a whole-atom relativistic effective core potential for the potassium cation provides the most accurate picture of its electronic structure without increasing the complexity of the calculation and its computational demand.