Calculation of the magnetic anistropy energy MAE within energy and force approaches (from wien mailing list )

[Wien] Query about SOC in WIEN2k

Rajiv Chouhan Fri, 04 Nov 2016 22:26:52 -0700

Dear Dr. P. Blaha,

I am trying to calculate the magnetic anisotropy energy (MAE) for the
magnetic system Nd-metal. For this I tried couple of methods (energy
theorem and force theorem) to calculate MAE.

Energy theorem:

step-1: Performed GGA+U ; Step-2: executed initso_lapw  for different
directions 001, 100 etc ; Step-3: Didn't put RLO (relativistic local
orbital in the .inso file)

Step-4: Performed runsp_lapw -so -orb -dm  -ec 0.000001 ; Step-5 Took
the difference of energies E[001] - E[100]

The above method give correct result in very few cases. Am I doing wrong
somewhere?


Force Theorem:

Will you please explain the steps correctly because I am confused while
doing the steps. I followed the below steps and this is not working for me.

Step-1: Performed GGA+U (runsp_lapw -dm -orb -ec 0.000001);

Step-2: initso_lapw (by taking below actions)

---->Add RLO for NONE, ALL, CHOOSE elements? (N/a/c) : N

Do you have a spinpolarized case (and want to run symmetso) ? (y/N) Y

Do you want to use the new structure for SO calculations ? (y/N)   N

Step-3: x lapwso -up

Step-4: x lapw2 -up

Step-5: x lapw2 -dn

Step-6:  MAE = 001(sum of eigenvalues up & down) - 100(sum of
eigenvalues up & down)

This force method is also not working properly. Will you please correct
me where I am doing wrong.

I also followed the following links for my above steps:

https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09408.html

http://zeus.theochem.tuwien.ac.at/pipermail/wien/2010-September/013730.html

Thank you,
R. Chouhan

_______________________________________________

Answer of Prof Peter Blaha

Re: [Wien] Query about SOC in WIEN2k

Peter Blaha Sat, 05 Nov 2016 09:44:00 -0700

There are a lot of problems in your calculations: Usually the energy difference between 2 such calculations is extremely small and one must be very careful to get meaningful numbers. When you do initso for a spinpolarized system, the symmetry can be reduced. In such cases you MUST take the newly generated struct file. 

 > Do you want to use the new structure for SO calculations ? (y/N) N 

 This is the wrong answer !

 In fact, one should even do the calculations for the different magnetization directions with the same symmetry (eventually in P1). Thus checkout what symmetries you get for the different directions and choose the one which is compatible with all cases. Check your case.inorb/dmc files in case that the number of atoms has been changed. 

 Important: Increase Emax in case.in1 to a VERY large number (10 Ry), and test your results with respect to this EMAX. Increase the k-mesh (for the final low-symmetry struct file) to a very good one AND TEST the convergence. of your results. With such a struct file you run again (in the same directory) the non-so calculation to selfconsistency with a good k-mesh and good convergence: runsp -orb -ec 0.000001 -cc 0.000001 Since the E differences are very small, set the DEs in case.in1 to a smaller value like: 0 -4.09 .0001 STOP 1 ^^^^^^^ DE 

 Once the non-so calculation is converged: save_lapw non_so Now the force theorem: select 001 direction in case.inso x lapw1 -up/dn x lapwso -up -orb x lapw2 -so -up/dn cp case.scf2up/dn 001_kmesh_emax.scf2up/dn select other direction(s) and repeat the above steps. Compare the band energies listed in the scf2xx files. for the energy: select 001 direction runsp -so -orb -ec 0.000001 -cc 0.000001 save 001_kmesh_emax restore non_so do everything again for another direction. Make sure to check EMX and kmesh convergence. PS: I've never done MCA calculations using GGA+U !! 

Reference: https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg14847.html