Spin wave dispersion based on the quasiparticle self-consistent GW method:: NiO, MnO and α-MnAs

We present calculations of spin wave dispersions for antiferromagnetic MnO, NiO and ferromagnetic alpha-MnAs based on the recently developed quasiparticle self-consistent GW method (QSGW); we have already shown that QSGW gave a good quasiparticle picture for MnO and NiO in comparison with optical experiments. To obtain the spin wave dispersions, we have developed a method to calculate the transverse dynamical spin susceptibility in the random-phase approximation. This is a general method applicable not only to QSGW, but also to any first-principle method which gives the non-interacting (one-body) Hamiltonian to represent quasiparticles, e. g. the Kohn-Sham Hamiltonian in the density functional theory. In the method, we first calculate the non-interacting spin susceptibility from the supplied non-interacting Hamiltonian; then we obtain the spin susceptibility where the size of the effective interaction is determined so as to satisfy a sum rule. For MnO and NiO, the obtained spin wave dispersions show good agreement with experiments, in contrast to the cases in the local density approximation (LDA) and in the LDA + U. These results support our claim that the independent-particle picture is powerful enough even for materials like NiO and MnO classified to the Mott insulator, that is, the quasiparticle pictures by QSGW work well to describe their linear responses. For alpha-MnAs, we find a collinear ferromagnetic ground state in QSGW, while this phase is unstable in the LDA.