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I am doing simple scf calculation to find similarities in the output of VASP and QE. Recently, I encounter an interesting case. I took face-centred orthorhombic cell of Aluminium. Here is my POSCAR

Al
   4.05000000000000
     1.0300000000000000    0.0000000000000000    0.0000000000000000
     0.0000000000000000    0.9700000000000000    0.0000000000000000
     0.0000000000000000    0.0000000000000000    1.0000000000000000
   Al
     4
Direct
  0.0000000000000000  0.0000000000000000  0.0000000000000000
  0.5000000000000000  0.5000000000000000  0.0000000000000000
  0.0000000000000000  0.5000000000000000  0.5000000000000000
  0.5000000000000000  0.0000000000000000  0.5000000000000000

Here vasp code detects symmetry of orthorhomic cell with following symmetry operation (in OUTCAR)


 Subroutine INISYM returns: Found  8 space group operations
 (whereof  8 operations are pure point group operations),
 and found     4 'primitive' translations

Now using QE with following input

 &control
    calculation='relax'
    restart_mode='from_scratch',
    pseudo_dir ='.'
    outdir='./tmp/',
    prefix='al'
    tprnfor = .true.
    tstress = .true.
    disk_io='none'
 /
 &system
    ibrav=  0,A =4.05, nat=  4, ntyp= 1, ecutwfc =60,
    occupations='smearing', smearing='mv', degauss=0.02

 /
 &electrons
    diagonalization='cg'
    mixing_beta = 0.7
 /
&ions
ion_dynamics='bfgs'
/
CELL_PARAMETERS alat
1.03 0 0
0 0.97 0
0 0 1

ATOMIC_SPECIES
 Al  26.98 Al.pbe-n-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS alat
 Al 0.00 0.00 0.00
 Al 0.50 0.50 0.00
 Al 0.50 0.00 0.50
 Al 0.00 0.50 0.50
K_POINTS automatic
15 15 15  0 0 0

and output have shown following symmetry operation

      2 Sym. Ops. (no inversion) found

I have also test with ibrav=8, results are still same

Can somebody explain why QE is resulting only 2 point group operation in reality, it must have 8.

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  • 1
    $\begingroup$ The solution of this problem is by replacing ATOMIC_POSITION alat to ATOMIC_POSITION crystal. Direct coordinate in CASE is equivalent to QE crystal not alat. we can close this question now $\endgroup$
    – Pranav kumar
    Nov 6, 2021 at 1:20
  • 1
    $\begingroup$ Did you vote to close it? If you found the answer, please write it as an answer. $\endgroup$
    – Nike Dattani
    Nov 6, 2021 at 4:42

1 Answer 1

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VASP input file is based on relative coordinates(direct) of the simulation box whereas in QE alat doesn't define relative coordinate, It only scale by lattice parameter. In QE relative coordinate is defined by atomic position tag crystal. Correct input file for 8 different symmetry operations will be

 &control
    calculation='relax'
    restart_mode='from_scratch',
    pseudo_dir ='.'
    outdir='./tmp/',
    prefix='al'
    tprnfor = .true.
    tstress = .true.
    disk_io='none'
 /
 &system
    ibrav=  0,A =4.05, nat=  4, ntyp= 1, ecutwfc =60,
    occupations='smearing', smearing='mv', degauss=0.02

 /
 &electrons
    diagonalization='cg'
    mixing_beta = 0.7
 /
&ions
ion_dynamics='bfgs'
/
CELL_PARAMETERS alat
1.03 0 0
0 0.97 0
0 0 1

ATOMIC_SPECIES
 Al  26.98 Al.pbe-n-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS crystal
 Al 0.00 0.00 0.00
 Al 0.50 0.50 0.00
 Al 0.50 0.00 0.50
 Al 0.00 0.50 0.50
K_POINTS automatic
15 15 15  0 0 0
```
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  • $\begingroup$ +1 and thanks for writing the answer when you figured it out, so that it can help future readers! I'd recommend not to put a green checkmark on your own answer, because unlike when you put a green checkmark on a different person's answer, the green checkmark doesn't have much of an effect other than discouraging others from writing alternative answers! $\endgroup$
    – Nike Dattani
    Nov 11, 2021 at 19:57

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