Assessing the Global Natural Orbital Functional Approximation on Model Systems with Strong Correlation

In the past decade, natural orbital functional (NOF) approximations haveemerged as prominent tools for characterizing electron correlation. Despitetheir effectiveness, these approaches, which rely on natural orbitals and theirassociated occupation numbers, often require hybridization with other methodsto fully account for all correlation effects. Recently, a global NOF (GNOF) hasbeen proposed [Phys. Rev. Lett. 127, 233001 (2021)] to comprehensively addressboth dynamic and static correlations. This study evaluates the performance ofGNOF on strongly correlated model systems, including comparisons with highlyaccurate Full Configuration Interaction (FCI) calculations for hydrogen atomclusters in one, two, and three dimensions. Additionally, the investigationextends to a BeH2 reaction, involving the insertion of a beryllium atom into ahydrogen molecule along a C2v pathway. According to the results obtained usingGNOF, consistent behavior is observed across various correlation regions,encompassing a range of occupation and orbital schemes. Furthermore,distinctive features are identified when varying the dimensionality of thesystem.