1
$\begingroup$

I'm a newbye in DFT calculations and it's my first time I use vc-relax. I have to find optimal cell parameters for mono-layer $MoS_2$ and that's my code :

      &CONTROL
calculation = 'vc-relax'
prefix = 'MoS2_MonoLayer '
pseudo_dir = './'
outdir = './'
tsress=.true.
tprnfor=.true.
forc_conv_thr = 1.0d-3
nstep = 200
/
      &SYSTEM
ibrav = 4
a = 3.244249522500000
c = 9.365949096500000
nat = 3
ntyp = 2
ecutwfc = 50
ecutrho = 310
/
        &ELECTRONS
mixing_beta = 0.7
conv_thr = 1.0 d-8
diagonalization = 'david'
electron_maxstep = 200
/
     &IONS
trust_radius_max = 0.2
/
     &CELL
cell_dynamics = "bfgs"

ATOMIC_SPECIES
Mo 95.9400 Mo.pbesol-spn-kjpaw_psl.1.0.0.UPF
S 32.0660 S.pbesol-n-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS(crystal)
Mo 0.333333330 0.666666670 0.250000000
 S 0.666666670 0.333333330 0.087698981
 S 0.666666670 0.333333330 0.412301018

K_POINTS{automatic}
4 4 4 0 0 0

I never get that nice "JOB DONE" using vc-relax , this only works with scf. Sometimes I get the error dE0s is positive which it should never happen. I really do not know what to do :(

$\endgroup$
3
  • 1
    $\begingroup$ How many processors is you system using and how much time are you giving it? Usually vc-relax takes a lot of time even with 8-12 procesors $\endgroup$ Jul 13, 2023 at 11:23
  • $\begingroup$ I was giving 8 processor but still had trouble. But the main problem Is that now I cannot write even .out file with scf method :/ $\endgroup$ Jul 13, 2023 at 12:35
  • $\begingroup$ Are you sure that the parameters that you are using are correct? Because I tested your input file, and found that the forces get to a minimum value very quickly but then keeps oscillating. $\endgroup$ Jul 14, 2023 at 6:15

1 Answer 1

1
$\begingroup$

I used the following input file (I made few changes; like using the default values for convergence and other parameters, and used a larger cutoff for ecutrho and ecutwfn). I was able to get the file to converge in 21 bfgs cycles.

 &CONTROL
   title           = 'test-mos2' 
   calculation     = 'vc-relax' 
   restart_mode    = 'from_scratch' 
   outdir          = './temp' 
   pseudo_dir      = './' 
   prefix          = 'MoS2_MonoLayer' 
   disk_io         = 'high' 
   verbosity       = 'high' 
   tstress         = .true. 
   tprnfor         = .true. 
 /
 &SYSTEM
   ibrav           = 4
   A               = 3.244249522500000 
   C               = 9.365949096500000 
   nat             = 3
   ntyp            = 2
   ecutwfc         = 60 
   ecutrho         = 600 
   nbnd            = 20
 /
 &ELECTRONS
   startingpot     = 'atomic' 
   startingwfc     = 'atomic+random' 
   mixing_mode     = 'plain' 
   diagonalization = 'david' 
 /
 &IONS
   ion_dynamics    = 'bfgs' 
   pot_extrapolation = 'atomic' 
   wfc_extrapolation = 'first_order' 
 /
 &CELL
   cell_dynamics   = 'bfgs' 
   cell_dofree     = 'all' 
 /
ATOMIC_SPECIES
   Mo   95.94000  Mo.pbe-spn-kjpaw_psl.1.0.0.UPF 
    S   32.06600  S.pbe-n-kjpaw_psl.1.0.0.UPF 
ATOMIC_POSITIONS crystal 
   Mo      0.333333330    0.666666670    0.250000000    
    S      0.666666670    0.333333330    0.087698981    
    S      0.666666670    0.333333330    0.412301018    
K_POINTS automatic 
  4 4 4   0 0 0 
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .