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 explicitly considered, especially when considering the 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 PtCl₄ ^2- including counter-ion 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. PtCl₄ ^2- is investigated as a charged gas phase complex, a point-charge-neutralized complex, and a pseudopotential-neutralized complex. Results indicate that the use of a whole-atom relativistic effective core potential for the potassium cation provides a more accurate representation of the environment than a point charge and accurately represents electronic states without increasing the complexity of the calculation and, therefore, its computational demand.