$B1$-to-$B8$ structural phase transition in MnO under pressure: Comparison of all-electron and pseudopotential approaches

We employ the density-functional theory to study a structural transition of MnO from $B1$ (rocksalt) to $B8$ (NiAs) structures that was observed experimentally at pressures around $100\mathrm{GPa}$. We utilize all-electron description as well as norm-conserving pseudopotentials and demonstrate that these two approaches can significantly differ in quantitative predictions. We explicitly show that even small-core pseudopotentials exhibit transferability inaccuracies for quantities sensitive to the energy differences between high- and low-spin polarizations of valence electrons.

Figure 1

(Color online) Difference between all-electron and pseudopotential total energies [Eq. (2)], as calculated for the $B1$ AFM structure within LAPW PBE-GGA method (bullets). Also shown is magnetic moment on the Mn atom with all-electron core (full squares) and YN pseudopotential (empty squares). The slight enhancement of local moments when pseudopotentials are introduced, visible also in Tables , is consistent with other reports (Refs. 13, 32). Volumes at the transition to the $B8$ FM phase are indicated as well.

Figure 2

(Color online) Same quantities as in Fig. 1 but for $B8$ FM structure.

Figure 3

(Color online) Total energies of $B1$ AFM (circles) and $B8$ FM (squares) phases as they depend on the volume for the LAPW PBE-GGA method. Both all-electron (filled symbols) and pseudopotential (empty symbols) data are shown together with the corresponding double tangents illustrating the respective transition pressures.

Figure 4

(Color online) Magnetic moment on Mn atom in $B1$ AFM (empty squares) and $B8$ FM (full squares) phases as calculated using the $\mathrm{PBE}{0}_{10}$ functional. Values are taken from YN PP calculation; corresponding all-electron data are virtually indistinguishable. Transition volumes are shown as well. The small skip around $V=14.4{\mathrm{\AA }}^3$ is related to a more rapid transfer of occupation between the majority and minority bands that takes place at this volume. It occurs both in all-electron and pseudopotential data, and therefore it has no impact on the subject discussed in this study. No such skip is observed in the $B8$ AFM phase.