Active Space Pair 2-Electron Reduced Density Matrix Theory for Strong Correlation
Abstract
An active space variational calculation of the 2-electron reduced density matrix (2-RDM) is derived and implemented where the active orbitals are correlated within the pair approximation. The pair approximation considers only doubly occupied configurations of the wavefunction which enables the calculation of the 2-RDM at a computational cost of . Calculations were performed both with the pair active space configuration interaction (PASCI) method and the pair active space self consistent field (PASSCF) method. The latter includes a mixing of the active and inactive orbitals through unitary transformations. The active-space pair 2-RDM method is applied to the nitrogen molecule, the p-benzyne diradical, a newly synthesized BisCobalt complex, and the nitrogenase cofactor FeMoco. The FeMoco molecule is treated in a [120,120] active space. Fractional occupations are recovered in each of these systems, indicating the detection and recovery of strong electron correlation.
Cite
@article{arxiv.2005.07168,
title = {Active Space Pair 2-Electron Reduced Density Matrix Theory for Strong Correlation},
author = {Kade Head-Marsden and David A. Mazziotti},
journal= {arXiv preprint arXiv:2005.07168},
year = {2020}
}