Pair‐Density Functional Theory Based on Spin‐Projected Unrestricted Hartree‐Fock Method: A Density‐Corrected Version

Achieving an accurate yet computationally efficient treatment of both static and dynamic electron correlation remains a central challenge in quantum chemistry. This work introduces a density-corrected (DC) version of the recently proposed pair-density functional theory based on the spin-projected unrestricted Hartree-Fock method (SU-PDFT). SU-PDFT combines spin-projected unrestricted Hartree-Fock (SUHF) with an on-top pair-density functional, offering a cost-effective alternative to multiconfiguration pair-density functional theory (MC-PDFT). While SU-PDFT provides moderate accuracy, it exhibits significant errors for properties such as spin splittings and transition-metal bond dissociation energies. Inspired by density-corrected DFT, we proposed here the density-corrected SU-PDFT (DC-SU-PDFT) method, which incorporates a density functional theory contribution in the self-consistent step, yielding a pseudo-spin density of higher quality. Benchmarks demonstrate that DC-SU-PDFT generally improves upon SU-PDFT for spin splittings, bond dissociation energies of diatomic molecules, and isomerization energies, achieving an overall accuracy comparable to that of MC-PDFT while retaining a favorable computational cost.