A Two-Step Rayleigh-Schr\"odinger Brillouin-Wigner Approach to Transition Energies

• URL: http://arxiv.org/abs/2311.08356v1
• Date: Tue, 14 Nov 2023 17:58:24 GMT
• Title: A Two-Step Rayleigh-Schr\"odinger Brillouin-Wigner Approach to Transition Energies
• Authors: Loris Delafosse, Amr Hussein, Saad Yalouz, Vincent Robert
• Abstract summary: A two-step perturbative approach is introduced combining multi-state Rayleigh-Schr"odinger schemes and state-specific Brillouin-Wigner schemes. The first step produces model functions and an updated definition of the perturbative partitioning of the Hamiltonian. The second step inherits the improved starting point provided in the first step, enabling then faster processing of the perturbative corrections for each individual state.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Perturbative methods are attractive to describe the electronic structure of molecular systems because of their low-computational cost and systematically improvable character. In this work, a two-step perturbative approach is introduced combining multi-state Rayleigh-Schr\"odinger (effective Hamiltonian theory) and state-specific Brillouin-Wigner schemes to treat degenerate configurations and yield an efficient evaluation of multiple energies. The first step produces model functions and an updated definition of the perturbative partitioning of the Hamiltonian. The second step inherits the improved starting point provided in the first step, enabling then faster processing of the perturbative corrections for each individual state. The here-proposed two-step method is exemplified on a model-Hamiltonian of increasing complexity.

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