Extension of the fourfold way for calculation of global diabatic potential energy surfaces of complex,multiarrangement,non-Born-oppenheimer

摘要

The fourfold way is a generalal gorithm for generating diabatic electronic wave functions that span the same space as a small set of variationally optimized adiabatic electronic wave functions and for using the resulting diabatic wave functions to generate diabatic potential energy surfaces and their couplings. In this paper we extend the fourfold way so it is applicable to more complex polyatomic ssystems and in particular to the calculation of global potential energy surfaces for such systems. The systems and in particular to the calculation of global potentialenergy surfaces for such systems. The extension involves partitioning the active space into three blocks,introducing restricted orbital rotation within two of the blocks,introducing a specific resolution of subspace containing molecular orbitals that are doubly occupied in all dominant configuration state functions,and introducing specific orientations of the coordinate systems for reference moelcular orbitals and resolution molecular orbitals. The major strengthof the improved method presented in this paper is that it allows the diabatic molecular obitals to exhibit a gradual change of chemical character with smooth deformation alog the reaction coordiante for a change of chemical arrangement while smooth deformation along the reaction coordinate for a change of chemical arrangement while preserving the orbital character required for a physical ordering of the orbitals. This feature is required for the convenient construction of global potential energy surfaces for non-Born-Oppenheimer rearrangements. The resulting extendd algorithm is illustrated by calculating diabatic potential energy surfaces and couplings for the two lowest singlet potential energy surfaces of HNCO.