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The exchange-correlation (XC) potential is the central quantity in Kohn-Sham density functional theory (KS-DFT) and fully determines the accuracy of electronic structure calculations. We are developing a novel method, termed spatial mixing of model potentials (SMMP), to obtain reliable, first-principles XC potentials for challenging systems. The method is formulated within the hybrid-DFT framework, and the XC potentials are constructed by mixing the local density approximation (LDA) and exact exchange (EXX) potentials, with spatially dependent mixing parameters derived from the piecewise linearity conditions of both the energy and the electron density.[1,2] SMMP holds strong promise for predicting electronic structures in challenging systems, such as charge-transfer systems, systems with unpaired electrons (e.g., radicals, anions, and polarons), and mixed-valence systems. SMMP is illustrated in the following figures.
Figure 1. The contour plot of the mixing parameter of CO molecule, from Ref. [1]
Figure 1 demonstrates the mixing parameter of the CO molecule. The method produces a mixing parameter with the correct asymptotic behavior, that is, it approaches one in carbon's vacuum region (where CO's HOMO dominates).
Figure 2. Ionization energies of various molecules, radicals, and anions, predicted by our new method, compared against CCSD(T) results, from Ref. [1]
Figure 2 shows that the new method predicts more accurate HOMO eigenvalues for various molecular systems, especially many challenging anions.
Figure 3. Kohn-Sham correlation potentials and mixing parameters of Be calculated using SMMP, LDA, and PBE. The atom is at x = 0 bohr.
Figure 3 shows that the new method can semi-quantitatively reproduce the Kohn–Sham correlation potentials, a very challenging task for XC functionals.
[1] C. Huang, J. Chem. Phys. 161, 084103 (2024)
[2] C. Huang, J. Chem. Phys. 163, 154104 (2025)
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