Charge localization in diatomic ions investigated with a dipole driven approach. II. Interplay with the spin-orbit coupling and polarization models, test for (KrXe).

Recently, we have proposed a method for the construction of charge-localized (approximately diabatic) basis sets of mixed rare-gas dimer cations based on the point-charge approximation of the dimer dipole moment matrix and applied it to the (NeAr)+ molecular ion [M. Ćosićová et al., J. Chem. Phys. 163, 044303 (2025)]. In the present paper, the method is extended to be applicable to heavier rare gases, and a specific application to (KrXe)+ is presented. The extension of the original method mainly consists in considering (a) relativistic effects (the spin-orbit coupling, in particular) in the electronic cloud of the studied system and (b) the polarizability of rare-gas atoms, both extensions being important for heavy rare gases. High-level ab initio calculations using multi-reference configuration interaction methods have been performed to obtain accurate inputs to the proposed charge-localization scheme and compared with available literature data.