Enhancing density-functional theory for static correlation in large molecules

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(N3) 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(N3) computational scaling of DFT while enabling the accurate treatment of static correlation for a broad range of molecules and materials.