Discontinuities of the exchange-correlation kernel and charge-transfer excitations in time-dependent density-functional theory
نویسندگان
چکیده
We identify the key property that the exchange-correlation (XC) kernel of time-dependent density-functional theory must have in order to describe long-range charge-transfer excitations. We show that the discontinuity of the XC potential as a function of particle number induces a spaceand frequency-dependent discontinuity of the XC kernel that diverges as r → ∞. In a combined donor-acceptor system, the same discontinuity compensates for the vanishing overlap between the acceptor and donor orbitals, thereby yielding a finite correction to the Kohn-Sham eigenvalue differences. This mechanism is illustrated to first order in the Coulomb interaction.
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