Bilinear Constraints upon the Correlation Contribution to the Electron-Electron Repulsion Energy as a Functional of the One-Electron Reduced Density Matrix

Jerzy Cioslowski; Zsuzsanna É Mihálka; Ágnes Szabados

doi:10.1021/acs.jctc.9b00443

Bilinear Constraints upon the Correlation Contribution to the Electron-Electron Repulsion Energy as a Functional of the One-Electron Reduced Density Matrix

J Chem Theory Comput. 2019 Sep 10;15(9):4862-4872. doi: 10.1021/acs.jctc.9b00443. Epub 2019 Aug 7.

Authors

Jerzy Cioslowski¹, Zsuzsanna É Mihálka^{2

3}, Ágnes Szabados²

Affiliations

¹ Institute of Physics , University of Szczecin , Wielkopolska 15 , 70-451 Szczecin , Poland.
² Laboratory of Theoretical Chemistry, Institute of Chemistry, Faculty of Science , ELTE Eötvös Loránd University , POB 32, H-1518 Budapest , Hungary.
³ Hevesy György Ph.D. School of Chemistry, Faculty of Science , ELTE Eötvös Loránd University , POB 32, H-1518 Budapest , Hungary.

PMID: 31294976
DOI: 10.1021/acs.jctc.9b00443

Abstract

Perturbative analysis of the functional U[n, ψ] that yields the correlation component U of the electron-electron repulsion energy in terms of the vectors ψ(1) and n of the natural spinorbitals and their occupation numbers (the 1-matrix functional) facilitates examination of the flaws inherent to the present implementations of the density matrix functional theory. Recognizing that the practical usefulness of any approximate 1-matrix functional hinges upon its capability of exactly reproducing the leading contribution to U at the limit of vanishing electron-electron interactions gives rise to asymptotic bilinear constraints for the (exact or model) 2-cumulant ${}^{2}G$ that enters the expression for U. The asymptotic behavior of certain blocks of ${}^{2}G$ is found to be equally important. These identities, which are obtained for both the single-determinantal and a model multideterminantal cases, take precedence over the linear constraints commonly enforced in the course of approximate construction of such functionals. This observation reveals the futility of designing sophisticated approximations tailored for the second-order contribution to ${}^{2}G$ while neglecting proper formulation of the respective first-order contribution that in the case of the so-called JKL-only functionals requires abandoning the JK-dependence altogether. It has its repercussions not only for the functionals of the PNOF family but also for the expressions involving only the L-type two-electron repulsion integrals (in the guise of their exchange counterparts) that account only for the correlation effects due to electrons with antiparallel spins and are well-defined only for spin-unpolarized and high-spin systems (yielding vanishing U for the latter).