fcc Ni revisited

Based on the VASP wiki example in this link

Task: Calculate partial DOS of spin-polarized fcc ferromagnet Ni.

First, copy the example folder which contains some of the VASP input files

``````cp -r /software/sse/manual/vasp/training/ws2020/fcc_Ni_rev .
cd fcc_Ni_rev``````

and copy the latest POTCAR file for Ni

``cp /software/sse/manual/vasp/POTCARs/PBE/2015-09-21/Ni/POTCAR .``

Input files

POSCAR

``````fcc Ni
-10.93
0.5 0.5 0.0
0.0 0.5 0.5
0.5 0.0 0.5
Ni
1
cartesian
0 0 0``````
• Note the use of volume instead of lattice parameter in the 2nd line, indicated by "-"

INCAR

``````SYSTEM  = Ni fcc bulk

ISTART  = 0
ISPIN   = 2
MAGMOM  = 1.0
ISMEAR  = -5
VOSKOWN = 1
LORBIT  = 11``````
• ISTART=0, start job from scratch (default)
• ISPIN=2, gives a spin-polarized calculation
• MAGMOM=1.0, an initial magnetic moment of 1.0 Bohr magnetons is set
• ISMEAR=-5, Tetrahedron method with Blöchl's corrections used for k-mesh integration
• VOSKOWN=1, interpolation scheme of Vosko, Wilk and Nusair applied
• LORBIT=11, write DOSCAR and lm-decomposed PROCAR

KPOINTS

``````k-points
0
Gamma
11 11 11
0  0  0``````
• Equally spaced k-mesh
• Here the Gamma (G) k-mesh is used, which always include the Gamma point

1. Collinear calculation

First create a new folder "col", copy the files and go there

``````mkdir col
cp INCAR POSCAR POTCAR KPOINTS run.sh col
cd col``````

since INCAR is already prepared for a collinear calculation, it's just to submit the job

``sbatch run.sh``

and it should finish quite quickly. Check the magnetic moment, e.g. by

``cat OSZICAR``

at the end it might look something like

``````...
DAV:   9    -0.545925473247E+01    0.23756E-02   -0.16066E-03  3008   0.279E-01    0.250E-01
DAV:  10    -0.545865706078E+01    0.59767E-03   -0.57805E-04  2004   0.147E-01    0.261E-02
DAV:  11    -0.545865295189E+01    0.41089E-05   -0.33171E-05  1412   0.519E-02
1 F= -.54586530E+01 E0= -.54586530E+01  d E =0.000000E+00  mag=     0.5874``````

Notice the value for the magnetic moment on the right hand side. To just show last line, e.g. `grep mag OSZICAR`.

One can also check the l decomposed parts of the magnetic moment at the end of OUTCAR, e.g. open it with

``less OUTCAR``

and press `G` (that is `shift` `g`) to go to the end (quit with `q`). It looks like

`````` magnetization (x)

# of ion       s       p       d       tot
------------------------------------------
1       -0.007  -0.026   0.636   0.602``````
• What happens if one instead sets an initial magnetic moment of `MAGMOM = 0.0` or `MAGMOM = 2.0`?
• What can be said about the importance of setting appropriate initial magnetic moments?
• Check the spin-polarized DOS using p4vasp
• Any interesting messages in slurm-JOBID.out?

2. Non-collinear calculation

In the case of a non-collinear calculation, the magnetic moment will be allowed to point in three dimensions. Now, go back to the main folder "fcc_Ni_rev", create a new folder "nonc" and copy relevant files

``````mkdir nonc
cp INCAR POSCAR POTCAR KPOINTS run.sh nonc``````

For non-collinear calculations, one needs to change INCAR, uncomment the two lines for the collinear calculations

``````#ISPIN   = 2
#MAGMOM  = 1.0``````

and insert two lines

``````LNONCOLLINEAR = .TRUE.
MAGMOM        = 0.0 0.0 1.0    ``````

The default is LNONCOLLINEAR=.FALSE. To run non-collinear calculations, the VASP binary must also be changed to `vasp_ncl`, otherwise the job will crash. Edit the job script "run.sh" so that the last lines look like

``````#mpprun vasp_std
mpprun vasp_ncl``````

Run the calculation

``sbatch run.sh``

and check the magnetic moment in the same way as for 1. when it finishes. For OSZICAR it might look like

``````DAV:  10    -0.546407531955E+01    0.67997E-03   -0.80644E-05  7064   0.195E-01    0.291E-02
DAV:  11    -0.546409507244E+01   -0.19753E-04   -0.12794E-04  7588   0.126E-01
1 F= -.54640951E+01 E0= -.54640951E+01  d E =0.000000E+00  mag=    -0.0000     0.0000     0.5878``````

and at the end of OUTCAR

`````` magnetization (x)

# of ion       s       p       d       tot
------------------------------------------
1       -0.000   0.000  -0.000  -0.000

magnetization (y)

# of ion       s       p       d       tot
------------------------------------------
1        0.000  -0.000   0.000   0.000

magnetization (z)

# of ion       s       p       d       tot
------------------------------------------
1       -0.008  -0.027   0.637   0.602``````
• What happens by changing the direction of the initial magnetic moment, e.g. setting `MAGMOM = 1.0 0.0 0.0` or `MAGMOM = 0.0 1.0 0.0`?

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