We re-examine the commonly used density functional theory plus Hubbard \textit{U} (DFT+U) method for the case of non-collinear magnets. While many studies neglect to explicitly include the exchange correction parameter \textit{J}, or consider its exact value to be unimportant, here we show that in the case of non-collinear magnetism calculations the \textit{J} parameter can strongly affect the magnetic ground state. We illustrate the strong \textit{J}-dependence of magnetic canting and magnetocrystalline anisotropy by calculating trends in the magnetic lithium orthophosphate family LiMPO4 (M = Fe and Ni) and difluorite family MF2 (M = Mn, Fe, Co and Ni). Our results can be readily understood by expanding the usual DFT+U equations within the spinor scheme, in which the \textit{J} parameter acts directly on the off-diagonal components which determine the spin canting.
@article{arxiv.1011.0939,
title = {Issues with J-dependence in the LSDA+U method for non-collinear magnets},
author = {Eric Bousquet and Nicola Spaldin},
journal= {arXiv preprint arXiv:1011.0939},
year = {2025}
}