Modern density functional theory (DFT) calculations employ the Kohn–Sham system ofnoninteracting electrons as a reference, with all complications buried in the exchange-correlationenergy (E_XC). The adiabatic connection formula gives an exact expression forE-XC.We considerDFT calculations that instead employ a reference of strictly correlated electrons. We define a"decorrelation energy" that relates this reference to the real system, and derive the correspondingadiabatic connection formula. We illustrate this theory in three situations, namely, the uniformelectron gas, Hooke's atom, and the stretched hydrogen molecule. The adiabatic connection forstrictly correlated electrons provides an alternative perspective for understanding DFT andconstructing approximate functionals.
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