[Zurück]

L. Peters, I. Di Marco, P. Thunström, M.I. Katsnelson, A. Kirilyuk, O. Eriksson:
"Treatment of 4f states of the rare earths: The case study of TbN";
Physical Review B, 89 (2014), 205109.

The lattice constant, bulk modulus, and shear constant of TbN are calculated by means of density functional
theory (DFT) in the local density approximation (LDA) and generalized gradient approximation (GGA), with
4f states treated as valence electrons or core electrons. In addition, local Coulomb repulsions U are treated both
statically as in the LDA+U approach and dynamically as in the dynamical mean-field theory in the Hubbard-I
approximation. It is shown that all methods, except DFT-LDA with 4f electrons treated as either valence states,
produce lattice constants and bulk moduli in good agreement with experiment. In the LDA+U approach multiple
minima are found, and we focus on the competition between a state with cubic symmetry and a state obtained
from atomic Hund´s rules. We find the state with cubic symmetry to be 0.59 eV lower in energy than the Hund´s
rules state, while the opposite was obtained in previous literature. The shear constant is shown to be rather
sensitive to the theoretical method used, and the Hund´s rules state obtained in LDA+U is found to be unstable
towards tetragonal shear. As to the magnetism, we find that the calculation based on the Hubbard-I approximation
reproduces observations with the best accuracy. Finally, the spectral properties of TbN are discussed, together
with the general applicability of the different methods in describing rare-earth elements and compounds.

http://dx.doi.org/10.1103/PhysRevB.89.205109