A method is described to calculate correlation energy in atoms. The total wavefunction of ann-electron system is expressed as a linear combination of products ofn one-electron basis orbitals. This function gives a correlated description of the system. Under suitable restrictions it reduces to DODS and to splitshell description of closed-shell atoms or molecules. Energies of He atom, He-like ions and also of H− ion have been calculated including radial correlation only. The calculated electron affinity of H is better than earlier split-shell calculations. The result for He shows that the energy limit for radial correlation has been attained. For the other 2-electron ions radial correlation alone explains about one-third of the total correlation.