Orbital entanglement and correlation from pCCD-tailored coupled cluster wave functions

Wave functions based on electron-pair states provide inexpensive and reliable models to describe quantum many-body problems containing strongly-correlated electrons, given that broken-pair have been appropriately accounted for by, instance, a posteriori corrections. In this article, we analyse the performance of methods in predicting orbital-based correlation spectra. We focus (orbital-optimized) pair-coupled cluster Doubles (pCCD) ansatz with linearized coupled-cluster (LCC) correction. Specifically, scrutinize how entanglement measures can be determined from pCCD-tailored CC wave function. Furthermore, employ single-orbital entropy, orbital-pair mutual information, eigenvalue spectra two-orbital reduced density matrices benchmark LCC correction one-dimensional Hubbard model periodic boundary condition as well N$_2$ F$_2$ molecules against DMRG reference calculations. Our study indicates pCCD-LCC accurately reproduces patterns weak-correlation limit close their equilibrium structure. Hence, conclude predicts regime. strong-correlation stretched bonds, correction, generally, overestimates correlations.