Correlation energy in atomic systems. III. Configurations with 3d and 4s electrons

The correlation energy for systems containing 3d and 4s electrons has been examined making use of recently obtained Hartree-Fock energies for the elements from K to Zn. In addition to the expected pair correlation between 3d electrons, a large extrashell correlation has been found. These results make it desirable to re-examine the simple correlation model previously put forward. The relativistic correction for the elements in consideration has been discussed.