UGA-SSMRPT2 -- A Multireference Perturbation Theory Predicting Accurate Electronic Excitation Energies in Diverse Molecular Systems
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arXiv
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| Auteurs principaux: | , , , |
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| Format: | Preprint |
| Publié: |
2026
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| _version_ | 1866910011535392768 |
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| author | Chanda, Shamik Bhattacharjya, Pratyush Sen, Avijit Sen, Sangita |
| author_facet | Chanda, Shamik Bhattacharjya, Pratyush Sen, Avijit Sen, Sangita |
| contents | UGA-SSMRPT2, the spin-free perturbative analogue of Mukerjee's State-Specific Multireference Coupled Cluster Theory (MkMRCC) is known to be successful for size-extensive and intruder-free construction of dissociation curves. This work demonstrates that UGA-SSMRPT2 is also an accurate and computationally inexpensive framework for computing excitation energies. The method achieves near-chemical accuracy for the vast majority of $π\to π^*$, $n \to π^*$, charge-transfer, valence-Rydberg and Rydberg excited states commonly used for benchmarking electronic structure theories for excited states. Our results demonstrate that UGA-SSMRPT2 excitation energies lie within 0.20 eV of EOM-CCSD and/or well-established theoretical best estimates often surpassing the popular MRPT2 approaches like NEVPT2, CASPT2, and MCQDPT while typically requiring smaller active spaces. Its state-specific formulation circumvents the well-known intruder-state problem and eliminates the need for empirical parameters such as IPEA shifts in CASPT2. This work proposes UGA-SSMRPT2 as a robust, and scalable approach for modeling challenging electronic excited states. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_04420 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | UGA-SSMRPT2 -- A Multireference Perturbation Theory Predicting Accurate Electronic Excitation Energies in Diverse Molecular Systems Chanda, Shamik Bhattacharjya, Pratyush Sen, Avijit Sen, Sangita Chemical Physics Computational Physics Quantum Physics UGA-SSMRPT2, the spin-free perturbative analogue of Mukerjee's State-Specific Multireference Coupled Cluster Theory (MkMRCC) is known to be successful for size-extensive and intruder-free construction of dissociation curves. This work demonstrates that UGA-SSMRPT2 is also an accurate and computationally inexpensive framework for computing excitation energies. The method achieves near-chemical accuracy for the vast majority of $π\to π^*$, $n \to π^*$, charge-transfer, valence-Rydberg and Rydberg excited states commonly used for benchmarking electronic structure theories for excited states. Our results demonstrate that UGA-SSMRPT2 excitation energies lie within 0.20 eV of EOM-CCSD and/or well-established theoretical best estimates often surpassing the popular MRPT2 approaches like NEVPT2, CASPT2, and MCQDPT while typically requiring smaller active spaces. Its state-specific formulation circumvents the well-known intruder-state problem and eliminates the need for empirical parameters such as IPEA shifts in CASPT2. This work proposes UGA-SSMRPT2 as a robust, and scalable approach for modeling challenging electronic excited states. |
| title | UGA-SSMRPT2 -- A Multireference Perturbation Theory Predicting Accurate Electronic Excitation Energies in Diverse Molecular Systems |
| topic | Chemical Physics Computational Physics Quantum Physics |
| url | https://arxiv.org/abs/2602.04420 |