Calculations on different states of the Oxygen atom using Vasp code

In this tutorial we reproduce the calculations done in the following link:

https://www.vasp.at/vasp-workshop/slides/Handson1.tgz

The version used for this calculation is vasp5.4.1

1/ Required input files

a/ The POTCAR file

 what information can be found in the POTCAR file?

– pseudopotential description
– data that is required to regenerate the potential 
– number of valence electrons
– atomic mass
– required energy cutoff

b/ The KPOINTS file

- Determines how many k-points are used to sample the Brillouin zone
- For molecules or atoms only a single k-point is required

KPOINTS file: Gamma-point only

1                 !  one k-point
rec              !  in units of the reciprocal lattice vector
0 0 0 1        ! 3 coordinates and weight

- For atoms and molecules the Bloch theorem does not apply, hence there is no need to use more then one single k-point

- When more k-points are used, only the interaction between the atoms (which should be zero) is described more accurately

c/ The POSCAR and INCAR files

Determines the lattice vectors (Bravais lattice) and the coordinates (position of the atoms)

a single atom POSCAR file: 

O atom in a box
1.0                    ! universal scaling parameters
8.0 0.0 0.0        ! lattice vector a(1)
0.0 8.0 0.0        ! lattice vector a(2)
0.0 0.0 8.0        ! lattice vector a(3)
1                       ! number of atoms
cart                   ! positions in cartesian coordinates
0 0 0

INCAR steers the calculations:

SYSTEM = O atom in a box
ISMEAR =  0

2/ O atom: Non-polarized calculation

Create a repertory called Oatom and copy the input files in the repertory 1_1_O_atom

/Oatom> ls
INCAR  KPOINTS  POSCAR  POTCAR

a/Running vasp

/Oatom> vasp_gam
running on    1 total cores
 distrk:  each k-point on    1 cores,    1 groups
 distr:  one band on    1 cores,    1 groups
 using from now: INCAR    
 vasp.5.4.1 05Feb16 (build Feb 22 2019 13:34:35) gamma-only                    
 
 POSCAR found :  1 types and       1 ions
 scaLAPACK will be used
 LDA part: xc-table for Pade appr. of Perdew
 POSCAR, INCAR and KPOINTS ok, starting setup
 WARNING: small aliasing (wrap around) errors must be expected
 FFT: planning ...
 WAVECAR not read
 entering main loop
       N       E                     dE             d eps       ncg     rms          rms(c)
DAV:   1     0.401551970624E+02    0.40155E+02   -0.11086E+03    14   0.324E+02
DAV:   2     0.215084107556E+02   -0.18647E+02   -0.18376E+02    28   0.312E+01
DAV:   3     0.949309188625E+00   -0.20559E+02   -0.20463E+02    21   0.690E+01
DAV:   4    -0.301708029145E+00   -0.12510E+01   -0.11406E+01    14   0.208E+01
DAV:   5    -0.313224606252E+00   -0.11517E-01   -0.11489E-01    14   0.216E+00    0.296E-01
DAV:   6    -0.314529039381E+00   -0.13044E-02   -0.66941E-03    28   0.570E-01    0.138E-01
DAV:   7    -0.314614061640E+00   -0.85022E-04   -0.56234E-05    14   0.976E-02
   1 F= -.31461406E+00 E0= -.16035174E+00  d E =-.308525E+00
 writing wavefunctions

b/Restart vasp in same directory

when vasp is restarted the WAVECAR file is read and the run is continued from the previous wavefunctions (converging rapidly)

 /Oatom> vasp_gam
 running on    1 total cores
 distrk:  each k-point on    1 cores,    1 groups
 distr:  one band on    1 cores,    1 groups
 using from now: INCAR   
 vasp.5.4.1 05Feb16 (build Feb 22 2019 13:34:35) gamma-only                   
 
 POSCAR found :  1 types and       1 ions
 scaLAPACK will be used
 LDA part: xc-table for Pade appr. of Perdew
 found WAVECAR, reading the header
 POSCAR, INCAR and KPOINTS ok, starting setup
 WARNING: small aliasing (wrap around) errors must be expected
 FFT: planning ...
 reading WAVECAR
 the WAVECAR file was read successfully
 initial charge from wavefunction
 entering main loop
       N       E                     dE             d eps       ncg     rms          rms(c)
DAV:   1    -0.314677534001E+00   -0.31468E+00   -0.38262E-05    14   0.694E-02    0.274E-03
DAV:   2    -0.314677198205E+00    0.33580E-06   -0.63140E-07    28   0.611E-03
   1 F= -.31467720E+00 E0= -.16041488E+00  d E =-.308525E+00
 writing wavefunctions

3/ O atom: Polarized calculation

The O atom is an open shell system with 2 unpaired electrons add ISPIN=2 to the INCAR file remove WAVECAR and restart vasp (alternatively copy all input files from repertory  1_2_O_atomspin).


/Oatom> ls
INCAR  KPOINTS  POSCAR  POTCAR

/Oatom> vasp_gam
 running on    1 total cores
 distrk:  each k-point on    1 cores,    1 groups
 distr:  one band on    1 cores,    1 groups
 using from now: INCAR    
 vasp.5.4.1 05Feb16 (build Feb 22 2019 13:34:35) gamma-only                    
 
 POSCAR found :  1 types and       1 ions
 scaLAPACK will be used
 LDA part: xc-table for Pade appr. of Perdew
 POSCAR, INCAR and KPOINTS ok, starting setup
 WARNING: small aliasing (wrap around) errors must be expected
 FFT: planning ...
 WAVECAR not read
 entering main loop
       N       E                     dE             d eps       ncg     rms          rms(c)
DAV:   1     0.400395567364E+02    0.40040E+02   -0.96644E+02    32   0.265E+02
DAV:   2     0.152257545998E+02   -0.24814E+02   -0.23745E+02    64   0.263E+01
DAV:   3    -0.551256028319E+00   -0.15777E+02   -0.14559E+02    48   0.603E+01
DAV:   4    -0.125848182485E+01   -0.70723E+00   -0.67728E+00    32   0.139E+01
DAV:   5    -0.126277624940E+01   -0.42944E-02   -0.42933E-02    48   0.115E+00    0.653E+00
DAV:   6     0.160491316459E+00    0.14233E+01   -0.32344E+00    32   0.894E+00    0.150E+00
DAV:   7    -0.112789347628E+01   -0.12884E+01   -0.78234E-01    32   0.398E+00    0.394E-01
DAV:   8    -0.154023477923E+01   -0.41234E+00   -0.11140E-01    32   0.146E+00    0.235E-01
DAV:   9    -0.162635587161E+01   -0.86121E-01   -0.81754E-03    32   0.474E-01    0.115E-01
DAV:  10    -0.167204426562E+01   -0.45688E-01   -0.11876E-02    32   0.512E-01    0.617E-02
DAV:  11    -0.167236225463E+01   -0.31799E-03   -0.41280E-04    32   0.122E-01    0.158E-02
DAV:  12    -0.167269536890E+01   -0.33311E-03   -0.83752E-05    32   0.451E-02    0.117E-02
DAV:  13    -0.167302466244E+01   -0.32929E-03   -0.16508E-05    32   0.233E-02    0.581E-03
DAV:  14    -0.167302844688E+01   -0.37844E-05   -0.18489E-06    32   0.849E-03
   1 F= -.16730284E+01 E0= -.15958973E+01  d E =-.154262E+00  mag=     1.9999
 writing wavefunctions

average (electrostatic) potential at core
  the test charge radii are     0.7215
  (the norm of the test charge is              1.0000)
       1 -83.0352



 E-fermi :  -7.1157     XC(G=0):  -0.7679     alpha+bet : -0.1463


 spin component 1

 k-point     1 :       0.0000    0.0000    0.0000
  band No.  band energies     occupation
      1     -25.0882      1.00000
      2     -10.0834      1.00000
      3     -10.0834      1.00000
      4     -10.0834      1.00000
      5      -0.4933      0.00000
      6       1.8217      0.00000
      7       1.8302      0.00000
      8       1.8304      0.00000

 spin component 2

 k-point     1 :       0.0000    0.0000    0.0000
  band No.  band energies     occupation
      1     -21.8401      1.00000
      2      -7.0548      0.33333
      3      -7.0548      0.33333
      4      -7.0548      0.33333
      5      -0.3535      0.00000
      6       1.9889      0.00000
      7       1.9889      0.00000
      8       1.9889      0.00000

Results

eigenstates for spin up and spin down are calculated “separately” in LSDA they interact only via the effective local potential spin-up and spin-down potential

 in the OUTCAR file, one can see two spin componen

 the spin component 1 has 2 more electrons corresponding the a magnetization of 2 Bohr magneton


4/ O atom: Symmetry broken

In the GGA, most atoms are characterized by a symmetry broken solution
VASP however symmetrizes the charge-density according to the determined symmetry of the cell

check the OUTCAR file, which symmetry is VASP using

to lower the symmetry simply change the lattice parameters to 7.0 8.0 and 9.0 in the POSCAR file and reduce SIGMA to SIGMA=0.01 (INCAR file)

(alternatively copy all input files from 1_3_Oatomspinlow.

 /Oatom> vasp_gam
 .....
.....
 1 F= -.18910885E+01 E0= -.18910885E+01  d E =-.101356E-51  mag=     2.0000
 writing wavefunctions


Result

A much lower energy

NB: For more analysis check the previous file