We demonstrate that Boys-localized diabatic states do indeed exhibit small derivative couplings, as is required of quasidiabatic states. In doing so, we present a general formalism for calculating derivative couplings and analytic gradients for diabatic states. We then develop additional equations specific to the case of Boys-localized configuration-interaction singles (CIS)—in particular, the analytic gradient of the CIS dipole matrix—and we validate our implementation against finite-difference results. In a forthcoming paper, we will publish additional algorithmic and computational details and apply our method to the Closs energy-transfer systems as a further test of the validity of Boys-localized diabatic states.
Fatehi, S., Alguire, E., & Subotnik, J. E. (2013). Derivative couplings and analytic gradients for diabatic states, with an implementation for Boys-localized configuration-interaction singles. The Journal of Chemical Physics, 139(12), 124112. https://doi.org/10.1063/1.4820485
The Journal of Chemical Physics