A variation perturbation calculation to study the excited-state wavefunctions of atoms

A variation perturbation calculation using coupled Hartree-Fock (CHF) theory has been presented to study the excited-state wavefunctions of many-electron systems. The excited-state wavefunctions are extracted from the poles of an appropriate functional obtained from a linearised time-dependent response of the system under external frequency-dependent perturbation. The theory has been applied to find the excited n 1 S (n>1) functions of two-electron atomic systems. Excellent agreement is observed for the transition energies and matrix elements of different operators.