Communication: A mean field platform for excited state quantum chemistry

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Accurate prediction of molecular excited states is crucial for understanding photochemistry and spectroscopy.
• Existing methods often face challenges in balancing accuracy and computational cost for excited-state calculations.

Purpose of the Study:

• To introduce a novel mean-field theory for excited states, analogous to ground-state Hartree-Fock theory.
• To establish a foundation for developing advanced excited-state correlation methods.

Main Methods:

• A deterministic, state-specific mean-field approach is presented, employing a variational principle on a minimally correlated ansatz.
• The method relaxes the orbital basis and exhibits Fock-build cost-scaling.
• It is combined with an excited-state analog of second-order Møller-Plesset perturbation theory.

Main Results:

• The developed theory provides energy stationary points and serves as a basis for perturbation theory and coupled cluster methods.
• Calculations on water, formaldehyde, neon, and stretched lithium fluoride demonstrate high accuracy.
• The results significantly surpass Configuration Interaction Singles and are comparable to Equation of Motion Coupled Cluster methods.

Conclusions:

• The proposed mean-field theory offers a robust and accurate framework for excited-state calculations in quantum chemistry.
• This method provides a computationally efficient and accurate alternative for studying molecular excited states.