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?