Relativistic and Correlation Effects for Optical Levels of Large Atomic Systems: Application to Tl ii

Abstract

The effects of relativity and correlation on bound levels of large atomic systems are investigated by using the low‐Z Pauli approximation for the Hamiltonian. A linear combination of Slater determinants is used to approximate the wavefunctions. The radials are obtained from the Hartree–Fock–Slater equation with six potential forms, and the coefficients are found by application of the variational principle. Results are obtained for a matrix element involving any two configurations composed of a closed core and two valence spin–orbitals. Application is then made to some of the bound levels of Tl ii. The average error in the energy levels (the ground state is the reference level) is found to be 5% as compared to the average error of 25% in the nonrelativistic results of Beck. Both correlation and relativistic effects are important.