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Wavefunctions constructed from electron-pair states can accurately modelstrong electron correlation effects and are promising approaches especially forlarger many-body systems. In this article, we analyze the nature and the typeof electron correlation effects that can be captured by wavefunctionsrestricted to electron-pair states. We focus on the Antisymmetric Product of1-reference orbital Geminal (AP1roG) method combined with an orbitaloptimization protocol presented in [Phys. Rev. B, 89, 201106(R), 2014] whoseperformance is assessed against electronic structures obtained form DMRGreference data. Our numerical analysis covers model systems for strongcorrelation: the one-dimensional Hubbard model with periodic boundary conditionas well as metallic and molecular hydrogen rings. Specifically, the accuracy ofAP1roG is benchmarked using the single-orbital entropy, the orbital-pair mutualinformation as well as the eigenvalue spectrum of the one-orbital andtwo-orbital reduced density matrices. Our study indicates that contributionsfrom singly occupied states become important in the strong correlation regimewhich highlights the limitations of the AP1roG method. Furthermore, we examinethe effect of orbital rotations within the AP1roG model on correlations betweenorbital pairs.

Analysis of two-orbital correlations in wavefunctions restricted to electron-pair states