Write a PREreview

Spin-Pure Variational Energies and Spin Gaps for P450 Compound I across Correlated Active Spaces

by Uwe Bäcker

Posted: October 25, 2026
Server: Zenodo
DOI: 10.5281/zenodo.23651443

Variational selected-CI energies, Epstein–Nesbet PT2 corrections and exactly evaluated ⟨S²⟩ values for the sextet, quartet and doublet of Cytochrome P450 Compound I in the active spaces CAS(17,15), CAS(25,23) and CAS(33,31) of Goings et al. (PNAS 119, e2203533119, 2022). The doublets are spin-complete (⟨S²⟩ = 0.75000000) and remain strict variational upper bounds. With PT2, the spin gaps agree with the DMRG gaps of Goings et al. to within 0.0116 kcal/mol; in CAS(17,15) the energies agree with full CI to within 1 nHa. All variational energies lie below the UCCSD(T) energies of Goings et al. This version supersedes the previous one and corrects several of its statements (see manuscript, section "Corrections to v0.3"). Deposited: manuscript (PDF), wavefunctions, integrals and independent verification scripts for energy, ⟨S²⟩, PT2 and FCI; details in README.txt.

You can write a PREreview of Spin-Pure Variational Energies and Spin Gaps for P450 Compound I across Correlated Active Spaces. A PREreview is a review of a preprint and can vary from a few sentences to a lengthy report, similar to a journal-organized peer-review report.

Before you start

We will ask you to log in with your ORCID iD. If you don’t have an iD, you can create one.