Complete set of functions in the Heitler--London method for two-electron problem

Abstract It is shown that under certain restrictions the system of determinants φ i ( x 1 )φ k ( x 2 ) − φ k ( x 1 )ψ i ( x 2 ) constructed from two different sets of orbitals ψ k and φ k will be the complete set of functions for antisymmetrical two‐electron wave functions if the condition i < k is imposed.