> I am working on the magnetic properties of rare earth?iron > compounds. I have a question in structure optimization. > How to set the U and J parameters when using LDA+U method, since U > and J can?t be calculated by ab initio way? So I just set U=J=0. If > it is reasonable, then is it necessary to runsp_lapw with ??orb??
With U=J=0, you are doing a LDA calculation... That will not produce good results for rare earth-iron compounds. Check the literature to see what other people found to be meaningful U-values for rare earth-iron systems, for instance Torumba et al., PRB 74, 014409 (2006), http://link.aps.org/abstract/PRB/v74/e014409 Torumba et al., PRB 77, 155101 (2008), http://link.aps.org/abstract/PRB/v77/e085123 Tran et al., PRB 77, 85123 (2008), http://link.aps.org/abstract/PRB/v77/e155101 and references therein. If these U-values do not produce good results for your compounds, modify them (slightly) and see whether that improves the situation for you. Stefaan Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm