A critical challenge for density-functional theory (DFT) in practice is its limited ability to treat static electron correlation, leading to errors in its prediction of charges, multiradicals, and reaction barriers. Recently, we combined one- and two-electron reduced density-matrix theories with DFT to obtain a universal $O\left(N^3\right)$ generalization of DFT for static correlation. In this Letter, we enhance the theory's treatment of large molecules by renormalizing the trace of the two-electron identity matrix in the correction using Cauchy-Schwarz inequalities of the electron-electron repulsion matrix. We apply the resulting functional theory to linear hydrogen chains as well as the prediction of the singlet-triplet gap and equilibrium geometries of a series of acenes. This renormalization of the generalized DFT retains the $O\left(N^3\right)$ computational scaling of DFT while enabling the accurate treatment of static correlation for a broad range of molecules and materials.

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• Electronic structure of atoms & molecules
• Density functional theory
• Density matrix methods