Multi-configuration Hartree-Fock calculations III. Calculations of the 3P, 1D and 1S states arising from the 1s22s22p2 configuration for Z = 7$middot$0 to Z = 30$middot$0

Multi-configuration Hartree-Fock calculations are reported to study the term splitting in the 1s 2 2s 2 2p 2 configuration from Z = 7·0 to Z = 15·0. The wave functions include the Hartree-Fock configuration 1s 2 2s 2 2p 2 , the `quasi-degenerate' configuration 1s 2 2p 4 , the single replacement configurations 1s 2 2s3d2p 2 and 1s 2 2s 2 2p4f, the double replacement configurations from the 2p shell 1s 2 2s 2 3 l 3 l ′ ( l, l ′ = 0, 1, 2) and, finally, the intershell configuration 1s 2 2s3s2p3p. The separations of the 3 P, 1 D and 1 S levels predicted from these functions are in very good agreement with experiment not only for the ratio ( 3 P- 1 D)/( 1 D- 1 S) but also for the individual transitions. These functions have also been studied from Z = 6·0 to Z = 30·0 to compute the contribution to the correlation energy which arises from each configuration. For the 3 P and 1 D states the 1s 2 2s3d2p 2 configurations make a larger contribution to the correlation energy than does the 1s 2 2p 4 configuration at low Z . At higher Z the reverse is true. For the 1 S state all the configurations except the 1s 2 2p 4 configuration make a small contribution to the correlation energy throughout the isoelectronic series.