The Hartree approximation does not account for the exchange interaction under the interchange of particle coordinates. This problem was rectified by Fock with subsequent development of Hartree-Fock approximation 58 . This approximation assumes that electron exchange interaction can be written by the wave-function (Ψ HF ) which is defined as an antisymmetrised product of orbitals. Ψ HF is determined as a linear combination of 𝜓 𝑖 (𝒓 𝑖 𝜎 𝑖 ), which includes all permutations of the electron coordinates with the corresponding weights ±1. In 1951, Slater found that Ψ HF can be efficiently represented with N×N determinant which is defined as the Slater determinant ;