$\Delta$NO and the complexities of electron correlation in simple hydrogen clusters
Abstract
The NO two-electron density matrix (2-RDM) and energy expression are derived from a multideterminantal wave function. The approximate NO 2-RDM is combined with an on-top density functional and a double-counting correction to capture electron correlation. A trust-region Newton's method optimization algorithm for the simultaneous optimization of NO orbitals and occupancies is introduced and compared to the previous iterative diagonalization algorithm. The combination of NO and two different on-top density functionals, Colle-Salvetti (CS) and OF, is assessed on small hydrogen clusters and compared to density functional, single-reference coupled cluster, and multireference perturbation theory (MRMP2) methods. The NO-CS and NO-OF methods outperform the single-reference methods, and are comparable to MRMP2. However, there is a distinct qualitative error in the NO potential energy surface for H compared to the exact. This discrepancy is explained through analysis of the NO orbitals, occupancies and the two-electron density.
Keywords
Cite
@article{arxiv.2109.14129,
title = {$\Delta$NO and the complexities of electron correlation in simple hydrogen clusters},
author = {Ismael A. Elayan and Rishabh Gupta and Joshua W. Hollett},
journal= {arXiv preprint arXiv:2109.14129},
year = {2022}
}