We design a dynamically-weighted state-averaged constrained CASSCF to treat \ul{e}lectrons or \ul{h}oles moving between n molecular fragments (where n can be larger than 2). Within such a so-called eDSCn/hDSCn approach, we consider configurations that are mutually single excitations of each other, and we apply a generalized set of constraints to tailor the method for studying charge transfer problems. The constrained optimization problem is efficiently solved using a DIIS-SQP algorithm, thus maintaining computational efficiency. We demonstrate the method for a finite Su-Schrieffer-Heeger (SSH) chain, successfully reproducing the expected exponential decay of diabatic couplings with distance. When combined with a gradient, the current extension immediately enables efficient nonadiabatic dynamics simulations of complex multi-state charge transfer processes.
@article{arxiv.2508.21136,
title = {Fast Methods For Multisite Charge Transfer Processes I: Constrained, State Averaged CASSCF(1,M) and CASSCF(2M-1,M) Simulations},
author = {Tian Qiu and Joseph E. Subotnik},
journal= {arXiv preprint arXiv:2508.21136},
year = {2025}
}