Ground-state properties of lanthanum: Treatment of extended-core states

Three related techniques for performing accurate electronic-structure and total-energy calculations for systems with extended, so-called semicore, states are described. Total-energy calculations performed using the three methods are reported for fcc lanthanum. The convergence properties and relative accuracies of the three techniques are discussed. They are found to yield results in good agreement with each other and consistent with the available experimental data when well-converged calculations are performed. Highly accurate calculations are reported for the bcc phase, using one of these techniques, and a prediction of the bcc-fcc energy difference is reported.