Propagative Block Diagonalisation Diabatisation of DFT/MRCI Electronic States

TL;DR

This paper introduces a new propagative block diagonalisation method for calculating diabatic states within the DFT/MRCI framework, enabling the treatment of non-adiabatic effects in complex molecular systems.

Contribution

It develops a novel propagative block diagonalisation diabatisation approach compatible with DFT/MRCI, overcoming current limitations and allowing diabatic state calculations.

Findings

Successfully calculated diabatic potentials for LiH

Simulated vibronic spectrum of pyrazine accurately

Recovered non-adiabatic coupling effects

Abstract

We present a framework for the calculation of diabatic states using the combined density functional theory and multireference configuration interaction (DFT/MRCI) method. Due to restrictions present in the current formulation of the DFT/MRCI method (a lack of analytical derivative couplings and the inability to use non-canonical Kohn-Sham orbitals), most common diabatisation strategies are not applicable. We demonstrate, however, that diabatic wavefunctions and potentials can be calculated at the DFT/MRCI level of theory using a propagative variant of the block diagonalisation diabatisation method (P-BDD). The proposed procedure is validated {\it via} the calculation of diabatic potentials for LiH and the simulation of the vibronic spectrum of pyrazine. In both cases, the combination of the DFT/MRCI and P-BDD methods is found to correctly recover the non-adiabatic coupling effects of the problem.