Static Correlation Error

An error that arises in KS-DFT because it (KS-DFT) is based on a single Slater determinant. It is the inability of approximate KS-DFT (even with advanced XC functionals) to describe systems with entangled electronic configurations (mixtures of determinants) \[\ket{\Psi}=c_1\ket{\Phi_1}+c_2\ket{\Phi_2}+\cdots,\]

i.e. the wavefunction has multi-determinantal character.

As long as the basis is sufficiently large, a single Slater determinant from KS-DFT can reproduce the density \(n\) of a multideterminant method (like Configuration Interaction). However, the