FragPT2: Multi-Fragment Wavefunction Embedding with Perturbative Interactions

Embedding techniques allow the efficient description of correlations within localized fragments of large molecular systems, while accounting for their environment at a lower level of theory. We introduce FragPT2: a novel embedding framework that addresses multiple interacting active fragments. Fragm...

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Bibliographic Details
Published inarXiv.org
Main Authors Koridon, Emiel, Sen, Souloke, Visscher, Lucas, Polla, Stefano
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 08.08.2024
Subjects
Charge exchange
Charge transfer
Covalent bonds
Dimers
Embedding
Fragments
Molecular orbitals
Perturbation theory
Spin exchange
Wave functions
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Summary:Embedding techniques allow the efficient description of correlations within localized fragments of large molecular systems, while accounting for their environment at a lower level of theory. We introduce FragPT2: a novel embedding framework that addresses multiple interacting active fragments. Fragments are assigned separate active spaces, constructed by localizing canonical molecular orbitals. Each fragment is then solved with a multi-reference method, self-consistently embedded in the mean field from other fragments. Finally, inter-fragment correlations are reintroduced through multi-reference perturbation theory. Our framework provides an exhaustive classification of inter-fragment interaction terms, offering a tool to analyze the relative importance of various processes such as dispersion, charge transfer, and spin exchange. We benchmark FragPT2 on challenging test systems, including \ce{N_2} dimers, multiple aromatic dimers, and butadiene. We demonstrate that our method can be succesful even for fragments defined by cutting through a covalent bond.
ISSN:2331-8422