A comparison of computed and experimental neutron diffraction intensity at large momentum for MnO and NiO

Magnetic neutron scattering measures spin-spin correlations giving information about the long-range spin order as well as the shape of the spin density in magnetic materials. Similarly, detailed first principles calculations directly compute the spin density in materials. In this talk, I will show our careful comparison between experimentally measured magnetic neutron intensities and three levels of ab initio theory: density functional theory in two approximations, and diffusion Monte Carlo. While each theory performs similarly for the simple antiferromagnet MnO, there are significant differences between density functional theory and diffusion Monte Carlo in NiO. In each case, we show that diffusion Monte Carlo reduces the error with respect to the experiment. By connecting the intensities to the real-space spin density, we show that diffusion Monte Carlo reduces the error by spreading the spin density away from the core of the transition metal sites.

[1] A. Munoz et al., arXiv:2003.01183 (2020).