Non-adiabatic derivative coupling elements for the coupled cluster singles and doubles model

TL;DR

This paper introduces an efficient method for calculating non-adiabatic derivative coupling elements within the coupled cluster singles and doubles framework, enabling accurate analysis of conical intersections in complex molecules.

Contribution

It presents a novel biorthonormal formulation for derivative coupling calculations, contrasting with previous normalized state approaches, and demonstrates its application to thymine.

Findings

Successful computation of a conical intersection in thymine.

Enhanced efficiency in derivative coupling evaluations.

Potential for improved non-adiabatic dynamics simulations.

Abstract

We present an efficient implementation of analytical non-adiabatic derivative coupling elements for the coupled cluster singles and doubles model. The derivative coupling elements are evaluated in a biorthonormal formulation in which the nuclear derivative acts on the right electronic state, where this state is biorthonormal with respect to the set of left states. This stands in contrast to earlier implementations based on normalized states and a gradient formula for the derivative coupling. As an illustration of the implementation, we determine a minimum energy conical intersection between the n{\pi}* and {\pi}{\pi}* states in the nucleobase thymine.