Nonadiabatic Molecular Dynamics with Tight-Binding Fragment Molecular Orbitals

This work presents a nonadiabatic molecular dynamics methodology that relies on the use of fragment molecular orbitals computed using tight-binding Hamiltonians. The approach aims to model charge and energy transfer in large systems via quantum-classical trajectory-based approaches. The technique relies on a chemically motivated fragmentation of the overall system into arbitrary fragments. Several types of fragment molecular orbitals (FMO) can be constructed and used in nonadiabatic simulations, comprising quasidiabatic, adiabatic, and Löwdin-transformed ones. The adiabatic FMOs are found to be most suitable for modeling nonadiabatic dynamics in complex molecular systems. The overall algorithm shows advantageous scaling properties, making it possible to model long time scale charge transfer processes in large systems with many hundreds of atoms. The approach is applied to study charge transfer in subphtalocyanine(SubPc)/C₆₀ heterojunction. The computational results emphasize the importance of decoherence and details of interfacial structure for obtaining accurate charge transfer time scales in SubPc/C₆₀ herejunctions.