magnetic moment jumps to near 0 in large ni3al supercell with high accu

[browningcitori]

Hi everyone, I am having issues with the magnetic moment of ni3al supercells (96 atoms) with 1 rhenium impurity placed in the middle of the cell.

This doesn't happen when I set my accuracy lower:

With these settings:

SYSTEM = any
ISMEAR = 1
SIGMA = 0.2
ISIF = 2
PREC = ACCURATE
IBRION = 2
EDIFF = 1E-4
NSW = 30

LWAVE = .FALSE.
LCHARG = .FALSE.
MAGMOM = 96*2
ISPIN = 2
NELM = 100
IALGO = 48

I get:
16 F= -.53665681E+03 E0= -.53667131E+03 d E =-.872993E-03 mag= 10.4042


But, when accuracy is set to high with ENCUT set,

SYSTEM = any
ISMEAR = 1
SIGMA = 0.2
ISIF = 2
PREC = HIGH
IBRION = 2
EDIFF = 1E-4
NSW = 30
ENCUT = 350
LWAVE = .FALSE.
LCHARG = .FALSE.
MAGMOM = 96*2
ISPIN = 2
NELM = 100
IALGO = 48

I get:
3 F= -.53711021E+03 E0= -.53709487E+03 d E =0.152264E-02 mag= -0.4470


Does anyone know what is happening with this?

Thanks
<span class='smallblacktext'>[ Edited ]</span>

[jlbettis]

browningcitori,

Q1: Have you looked in the OUTCAR to ensure that the magnetic structure remains ferromagnetic? The magnetic structure may become antiferromagnetic. Hence, the net moment is Zero, but the local moment on each ion is non-zero.

Q2: What is ECUT set to in the first calculation?
Q3: What version of VASP are you using?

[browningcitori]

[quote="jlbettis"]browningcitori,

Q1: Have you looked in the OUTCAR to ensure that the magnetic structure remains ferromagnetic? The magnetic structure may become antiferromagnetic. Hence, the net moment is Zero, but the local moment on each ion is non-zero.

Q2: What is ECUT set to in the first calculation?
Q3: What version of VASP are you using?
[/quote]
Hi jlbettis,

1) I am not sure how to check this in the OUTCAR?

2) No ENCUT is set at all in the first calculation

3) I am using VASP 4.6

Thanks

[jlbettis]

browningcitori,

1) Assuming this is a Collinear Calculation. Open the OUTCAR file. Scroll towards the end of the file and look for a section labeled "magnetization (x)" it should look like the following:

magnetization (x)

# of ion s p d tot
----------------------------------------
1 -0.005 0.011 2.763 2.769
2 -0.005 -0.011 -2.763 2.769

The total column refers to the total local moment on an ion. As always the "# of the ion" corresponds to the ordering in the POSCAR.

2) You cannot compare relative energies of calculations that use different ENCUT-tag values. Search the OUTCAR of the first calculation and find what ENCUT value was used, I am almost certain is differs from the ENCUT value used in the 2nd calculation. The same ENCUT must be used in both calculations, regardless of choice of PREC-tag. Besides, if you define the ENCUT-tag in the INCAR-file there is no need to define the PREC-tag.

[browningcitori]

[quote="green"] magnetization (x)

# of ion s p d tot
----------------------------------------
1 -0.005 0.011 2.763 2.769
2 -0.005 -0.011 -2.763 2.769[/color]

The total column refers to the total local moment on an ion. As always the "# of the ion" corresponds to the ordering in the POSCAR.

2) You cannot compare relative energies of calculations that use different ENCUT-tag values. Search the OUTCAR of the first calculation and find what ENCUT value was used, I am almost certain is differs from the ENCUT value used in the 2nd calculation. The same ENCUT must be used in both calculations, regardless of choice of PREC-tag. Besides, if you define the ENCUT-tag in the INCAR-file there is no need to define the PREC-tag.[/quote]number?of?electron??789.0000000?magnetization??167.0000000
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[/code]



2) The ENCUT of the first calculation was 269eV as set by PREC = ACCURATE? I am guessing the PREC tag ONLY sets ENCUT? so When I Set ENCUT of 350 in the second one it overrides my "HIGH" setting?

I guess I should rephrase my question haha. In the first calculation with the ENCUT set to 269, the magnetic moment did not go to zero. But when I set ENCUT to 350 it did, I am wondering why this is?

Thanks again
<span class='smallblacktext'>[ Edited Wed Jul 18 2012, 09:21PM ]</span>

[jlbettis]

1) Literally, scroll to the end of the OUTCAR. Do not grep magnetization.

2) Maybe our choice of ENCUT?

ENCUT acts as the cut-off energy for the chosen pseudo pseudopotential. In general, ENCUT defines which orbitals are considered as valence. More orbitals are considered valence in your ENCUT = 269 calculation.

Judging from your grep of magnetization, the magnetization seems to steadily decreases throughout the calculation. How does the magnetization converge in the ENCUT = 269 and 350 eV calculations? Also, How does the charge converge in the ENCUT = 269 and 350 eV calculations? What else could we compare between the two calculations that may help us?

<span class='smallblacktext'>[ Edited Sun Jul 22 2012, 07:05PM ]</span>

[browningcitori]

[quote author= 269 calculation.

Judging from your grep of magnetization, the magnetization seems to steadily decreases throughout the calculation. How does the magnetization converge in the ENCUT = 269 and 350 eV calculations? Also, How does the charge converge in the ENCUT = 269 and 350 eV calculations? What else could we compare between the two calculations that may help us?

[/quote]</span>