Applicability of the no-pair equation with free-particle projection operators to atomic and molecular structure calculations

The no-pair equation with free-particle projection operators proposed by Sucher is employed for linear combination of atomic orbital calculations on one-electron atoms and a self-consistent-field configuration-interaction calculation of the ground-state energy and the spin-orbit splitting of the bromine atom. A matrix technique used for the representation of the required operators is discussed. Comparison of the results with Dirac-Hartree-Fock calculations shows that no-pair Hamiltonians furnish a convenient approximation for introducing relativistic effects in atomic and molecular structure calculations.