Relativistic one-electron approach to the effect of pressure on the magnetism ofEuCo2P2

Nonrelativistic and four-component relativistic electronic structure calculations with the discrete variational method within density functional theory were performed for embedded clusters representing the layered compound ${\mathrm{EuCo}}_{2}{\mathrm{P}}_{2},$ with ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type structure. A relativistic one-electron model based on Kramers degeneracy was devised to describe the observed changes in the magnetism of this compound induced by applied pressure, which include the collapse of the Eu moment and the formation of Co moments. The ${}^{151}\mathrm{Eu}$ M\"ossbauer isomer shift calculated with relativistic wave functions agrees well with experiment; however, the ${\mathrm{Eu}}^{2+}{\ensuremath{-}\mathrm{E}\mathrm{u}}^{3+}$ valence change previously proposed is not predicted.