Implications from Geometric Phase for Circulating Far Away Conical Intersection(s)

Area of Science:

• Quantum Chemistry
• Computational Chemistry

Background:

• Geometric phase phenomena are typically linked to conical intersections in molecular systems.
• The emergence of geometric phase far from conical intersections, especially for closed-shell configurations, remains an open question.

Purpose of the Study:

• To investigate the occurrence of geometric phase in nuclear configurations distant from conical intersections.
• To explore how closed-shell electronic configurations acquire a sign change upon completing a trajectory enclosing a conical intersection.

Main Methods:

• Full configuration interaction (FCI) calculations.
• Closed-shell single-reference calculations.
• Utilized toy models: H4 and LiH3.

Main Results:

• Conjectured that restricted Hartree-Fock (RHF) solutions encounter degeneracy points on closed loops encircling conical intersections.
• Observed that single-reference wave functions necessitate character changes near these degeneracy points.
• Indicated that multireference character is likely, even with substantial energy gaps between electronic states.

Conclusions:

• Geometric phase can manifest even when nuclear configurations are far from conical intersections.
• Degeneracy points encountered by RHF solutions are critical for understanding wave function behavior in such scenarios.
• The study highlights the importance of considering multireference character in electronic structure calculations under specific nuclear trajectories.