Density functional theory of crystal field quasiparticle excitations and the ab initio calculation of spin Hamiltonian parameters

We show, by carefully examining the change of total energy in constrained variational calculations using the local spin density approximation, that crystal field excitations in normal rare earths are quasiparticles composed of a 4f excitation plus its associated cloud of shielding conduction electrons. Total energy calculations, which properly exclude the self-interaction of the nonspherical part of the 4f densities, are then used to calculate crystal field energies and the corresponding spin Hamiltonian parameters of TmSb and PrSb, accurately from first principles.