Multistate metadynamics for automatic exploration of conical intersections

TL;DR

This paper presents a novel multistate metadynamics method that automatically explores conical intersection seams in molecular systems, aiding the understanding of photophysical and photochemical processes.

Contribution

The introduced multistate metadynamics method enables automatic exploration of conical intersections using energy gap as a collective variable, extending existing techniques.

Findings

Successfully applied to furan, revealing conical intersection landscapes.

Identifies minimum energy crossing points and barriers.

Can be integrated with various electronic structure methods.

Abstract

We introduce multistate metadynamics for automatic exploration of conical intersection seams between adiabatic Born-Oppenheimer potential energy surfaces in molecular systems. By choosing the energy gap between the electronic states as a collective variable the metadynamics drives the system from an arbitrary ground-state configuration toward the intersection seam. Upon reaching the seam, the multistate electronic Hamiltonian is extended by introducing biasing potentials into the off-diagonal elements, and the molecular dynamics is continued on a modified potential energy surface obtained by diagonalization of the latter. The off-diagonal bias serves to locally open the energy gap and push the system to the next intersection point. In this way, the conical intersection energy landscape can be explored, identifying minimum energy crossing points and the barriers separating them. We illustrate the method on the example of furan, a prototype organic molecule exhibiting rich photophysics. The multistate metadynamics reveals plateaus on the conical intersection energy landscape from which the minimum energy crossing points with characteristic geometries can be extracted. The method can be combined with the broad spectrum of electronic structure methods and represents a generally applicable tool for the exploration of photophysics and photochemistry in complex molecules and materials.