Accurate description of the nonadiabatic proton-coupled electron-transfer process in a diabatic representation: A model study

Abstract

Using a two-dimensional model system for the proton-coupled electron-transfer process, the eigenvalues and nonadiabatic dynamics have been notably investigated by means of diabatic representation in the Born-Oppenheimer picture. Different from a previously reported diabatic model, which was approximately determined by the eigenstates of the differently defined electronic Hamiltonians, the rigorous diabatization was achieved by a fitting method based on the adiabatic energies and derivative couplings. As expected, the rigorous diabatic models were found to be able to accurately reproduce the eigenvalues or nonadiabatic dynamics in the adiabatic representation for three different models. Furthermore, we proposed an approximate diabatic scheme, which was built from fitting the adiabatic energies solely but with a fixed form for the off-diagonal terms in the diabatic potential energy matrix. This approximate diabatic model without the aid of the derivative coupling is shown to be as accurate as the rigorous one, which provides a simple and efficient way to accurately describe the complex proton-coupled electron-transfer processes due to accurately computing derivative couplings that are quite challenging for realistic systems.