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Hello All:
I am trying to calculate magnetic anisotropy energy of bulk hcp Co
using spin-orbit coupling as a test case. I follow the instructions in
the VASP manual under the "LSORBIT tag". In particular, first I do a collinear
calculation and save the WAVECAR and CHGCAR files. Then I do a non-
collinear claculation by using the switch LSORBIT = .TRUE. I follow all
the other instructions given in the manual. However, I get results which
I do not understand. No matter what direction I choose for the spin
quantization axis, the spin moment is always directed along the z-axis.
Namely, for SAXIS=100, 001 and 111, spin moment is only along z. The
orbital moment is along SAXIS in every case.

Why is it so? Why should the spin and orbital moments be perpendicular to
each other in any case?

Thanks in advance for your help.

have you set ICHARG=11 in order to do one non-selfconsistent run?
please note that if you did not, vasp automatically converges to the magnetic ground state solution.

I did set ICHARG =11. Any other idea?

Do I need to set ISTART =1? I tried that also, but ran into the following problem:
LAPACK: Routine ZPOTRF failed!

So these calculations are with ISTART=0, ICHARG = 11. Is the value of ISTART the problem?

How to avoid the problem with ZPOTRF? Please note, I have done LSORBIT= TRUE calculations on another system with the same LAPACK libraries. So no problems with their installation.

Thanks.

[quote author= .TRUE. I follow all
the other instructions given in the manual. However, I get results which
I do not understand. No matter what direction I choose for the spin
quantization axis, the spin moment is always directed along the z-axis.
Namely, for SAXIS=100, 001 and 111, spin moment is only along z. The
orbital moment is along SAXIS in every case.

Why is it so? Why should the spin and orbital moments be perpendicular to
each other in any case?

Thanks in advance for your help. [/quote]


Actually, I am calculating the MAE of bcc Fe now, and I get the similiar result like you said, the spin moment is always in Z direction, the orbital moment is along SAXIS. Besides this, the totoal energy E001(SAXIS=001) and E111(SAXIS=111) are exactly the same ?

I really hope vasp experts can give some suggestions, thanks a lot