Nonadiabatic excited-state dynamics and energy gradients in the framework of FMO-LC-TDDFTB

TL;DR

This paper presents a new computational method combining FMO-LC-TDDFTB with Ehrenfest dynamics to simulate excited-state processes in large molecular systems, enabling detailed studies of exciton and charge transfer.

Contribution

The authors develop and implement excited-state gradients within FMO-LC-TDDFTB for nonadiabatic dynamics, expanding simulation capabilities for large molecular aggregates.

Findings

Validated the accuracy of analytical excited-state gradients.

Demonstrated application to exciton transport in organic semiconductors.

Showcased utility in charge-transfer dynamics in organic materials.

Abstract

We introduce a novel methodology for simulating the excited-state dynamics of extensive molecular aggregates in the framework of the long-range corrected time-dependent density-functional tight-binding fragment molecular orbital method (FMO-LC-TDDFTB) combined with the mean-field Ehrenfest method. The electronic structure of the system is described in a quasi-diabatic basis composed of locally excited and charge-transfer states of all fragments. In order to carry out nonadiabatic molecular dynamics simulatios, we derive and implement the excited-state gradients of the locally excited and charge-transfer states. Subsequently, the accuracy of the analytical excited-state gradients is evaluated. The applicability to the simulation of exciton transport in organic semiconductors is illustrated on a large cluster of anthracene molecules. Additionally, nonadiabatic molecular dynamics simulations of a model system of benzothieno-benzothiophene molecules highlight the methods utility in studying charge-transfer dynamics in organic materials. Our new methodology will facilitate the investigation of excitonic transfer in extensive biological systems, nanomaterials and other complex molecular systems consisting of thousands of atoms.