Similarity Constrained CC2: Toward Efficient Coupled Cluster Nonadiabatic Dynamics among Excited States

Area of Science:

• Quantum chemistry
• Theoretical chemistry
• Computational chemistry

Background:

• Standard coupled cluster models fail in nonadiabatic dynamics due to unphysical complex energies at conical intersections.
• Similarity constrained coupled cluster theory offers a viable approach for these simulations.

Purpose of the Study:

• To develop a similarity constrained perturbative doubles (SCC2) model for accurate nonadiabatic molecular dynamics.
• To ensure correct topography, topology, and real excitation energies at same-symmetry excited-state conical intersections.

Main Methods:

• Development of the similarity constrained perturbative doubles (SCC2) model.
• Application of the SCC2 model to conical intersections in hypofluorous acid and thymine.
• Comparison of SCC2 performance with existing computational methods.

Main Results:

• The SCC2 model yields real excitation energies and correct topographical features at conical intersections.
• The computational scaling remains favorable, similar to standard CC2.
• Accurate and efficient description of excited-state conical intersections is demonstrated.

Conclusions:

• The SCC2 model successfully addresses limitations of standard coupled cluster methods for nonadiabatic dynamics.
• This advancement enables accurate coupled cluster nonadiabatic dynamics simulations for large molecular systems.