Density functional scheme for calculating the ground-state pair density

Abstract We present an approximate scheme for calculating the pair density (PD) by means of the extended constrained-search theory. The single-particle equation of the auxiliary noninteracting system is derived on the basis of the variational principle with respect to the pair density. It is the modified Hartree–Fock (HF) equation that additionally contains the kinetic contribution of the exchange-correlation energy functional as the correlation term. The present scheme can provide a better total energy than that of the HF approximation.