I want to discuss one query regarding magnetic moment in my calculation. I am doing Eu doped WO3 calculation for different doping concentration having 2*2 supercell (128 atoms).
I am giving initial magnetic moment for Eu dopant. Sometime I get negative magnetic moment for any doping concentration or for same doping concentration with different convergence criteria. For example
When I choose convergence criteria as for 3.125 % doping concentration
EDIFF = 1.0e-04
EDIFFG = -0.02
then it is showing positive magnetic moment mag= 3.8483
When I am taking convergence criteria for same 3.125 % doping concentration
EDIFF = 1.0e-05
EDIFFG = -0.01
then it is showing -ve magnetic moment mag= -3.9682
Why is it so and what is the reason of negative magnetic moment ? How does remove negative magnetic moment ?
I took KPOINTS as
Automatic mesh
0
Gamma
2 2 3
0. 0. 0.
For other doping concentration I am getting -ve mag=-20 like that and difference in energy for same doping % but different convergence criteria upto 10.00 eV.
How do you expect the system to behave? is there some antiferromagnetic interaction, or ferrimagnetism? There should be no difference between a moment of -X and +X, as they are fully symmetric as long as the individual contributions also match.
I would advise you to set LORBIT = 11 and check the contributions of individual atomic sites.
But since you provide an initial moment for the Eu, the solution should always converge to the same value. Are you sure you set MAGMOM correctly?
Also, are the final energies the same in the two runs or does the tighter convergence criteria lead to more relaxations and a noticable lower energy? If this is the case then the first run was just not fully relaxed.
Dear Michael Wolloch, thank you for your suggestions !
I am taking Eu as a ferromagnetic since EuO is ferromagnetic after doping Eu in WO3 there is a possibility of making phase EuO. After your suggestions, I got clear my doubt all above problems were due to different convergence criterion. I will also check by LORBIT=11 for contributions of individual atomic sites.
My POSCAR contains
Eu W O
1 31 96
I am replacing 1 W atom by 1 Eu atom and so on for different doping concentration. I am taking initial magnetic moment 7.0 and in INCAR file as:
I am facing one problem in above calculation (Eu doped WO3). If my calculation run for any doping % is completing before wall time limit then it is giving energy value ok. But for some doping concentration if calculation is not converged and wall time is over then I am doing rerun calculation by
CONTCAR to POSCAR (with ISTART=0 without reading WAVECAR)
CONTCAR to POSCAR (with ISTART=1 with reading WAVECAR)
But in both cases in two different run I am getting energy after convergence more than last energy before wall time over in fresh run.
I got energy in first run -1136.46 eV
After wall time over and rerun calculation CONTCAR to POSCAR
I got energy -1128.36 eV
But energy should be lower than -1136.46 eV
I am doing DFT+U calculation for Eu and giving initial magnetic moment for Eu.
Strange. Double check if you start from the right WAVECAR and CONTCAR. Also Check if the magnetic situation is equivalent before and after restart. I think this is a simple workflow error and not some physics problem.