Extension of the fourfold way for calculation of global diabatic potential energy surfaces of complex, multiarrangement, non-Born-Oppenheimer systems: Application to HNCO(S₀, S₁)

A previous study proposed the fourfold way and systematic procedures for calculating global diabatic potential energy surfaces. As a continuation, an attempt was made to improve the fourfold way algorithm so that, while adhering to key elements introduced in previous work, it is applicable to more general and complex systems. A major strength of the resultant method is that it allows to obtain path-independent diabatic states even for chemical reactions by allowing smooth deformation of the diabatic molecular orbitals as the system moves from one arrangement to another.