The wave-function operator of coupled-cluster theory determines accurate wave functions, and derived electronic properties of molecular systems. This operator, often by spin-symmetry breaking, provides size-consistent calculations. We show this ability of the exponential-ansatz operator is preserved in single-particle density functional calculations, when the starting reference is the spin-symmetry broken Hartree-Fock wave function. The adapted, non-Hermitian, variational method is shown in this work to eliminate the fractional charges of well-known test cases, while maintaining a strong numerical consistency with traditional Kohn-Sham LDA calculations, where they perform well. We demonstrate with numerical calculations that this ansatz, within time-dependent DFT, facilitates the description of avoided-crossing regions, and the computation of quantum states where multiple electrons are optically excited.

Eliminating fractional charges in DFT calculations with the exponential ansatz

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