Dear, Recently I have calculated a system in cubic crystal structure (No.225, Fm-3m). The compound contains two magnetic ions A (0 0 0) and B (0.5 0.5 0.5). The experimental reported magnetic structure is each of the magnetic moments of A and B orders in the type I arrangement while the moment of A and B are antiparallel with each other. My first question is: when I design the magnetic structure as the experiment reported, the crystal structure reduced to be tetragonal (No.123, P4mmm). Will this symmetry reduction in calculation influence the results? Since my A ion is rare earth elements and the calculation from VASP (use the P1 symmetry) gets no magnetic moment for it. The earlier literatures have reported the magnetic moments of rear earth ions may be closely relative to the local crystal filed. Therefore I wonder whether the magnetic moment for the rare earth in my case from wien is reliable. My second question is: The magnetic moment of A ions converged to be parallel from GGA calculation (The spins have been inverted in case.inst file). To get the antiparallel magnetic moment of A ions. I do two GGA+U calculations. For the first one I do it based on the result from GGA calculation. The magnetic moment of A ions from this GGA+U calculation is sure to be parallel. For the other one I also use the GGA results. The difference is I use the case.dmat files from the first GGA+U calculation but invert the density matrix of the A ion whose spin has been inverted in case.inst file. Then I use ?-orbc? option. I did get antiparallel magnetic moment of A ions in the second calculation and the total energy is much lower than the first GGA+U calculation (about 3 Ry/f.u.). It that OK, or any problem? Any words will be appreciated! Best regards!
????????wangjingjing at ciac.jl.cn ??????????2011-04-28
