[QE-users] Regarding High Negative Pressure During vc-relax Calculation

[522mm1001 (Sankhasubhra Mukhopadhyay)]

Hello all,
       I am doing vc-relax calculation for the conventional cell NbCo2.
Everything going well, means convergence has been achieved with threshold
1e-8, but at the last step pressure comes with a high negative value like
-134 kbar. Same case occurs for both Ultrasoft and PAW pseudopotentials. I
am trying with different press_conv_thresholds,  but it comes the same
every time. I am giving my input file. Pls tell me where I should change?

&CONTROL
  calculation = 'vc-relax'
  outdir = './out/'
  prefix = 'NbCo2'
  pseudo_dir = '.'
  verbosity = 'high'
  etot_conv_thr = 1e-5
  forc_conv_thr = 1e-4
/
&SYSTEM
    degauss =   1d-02
    ibrav = 0,                   ! Free cell definition (explicit cell
parameters)
    nat = 24,                    ! Number of atoms in the unit cell
    ntyp = 2,                    ! Number of atomic species (Cr, Zr)
    ecutwfc = 50,                ! Wavefunction cutoff energy (Ry)
    ecutrho = 600,
    occupations = 'smearing'
    smearing = 'mp'
/
&ELECTRONS
    conv_thr = 1.0d-8,           ! Convergence threshold for SCF iterations
    electron_maxstep = 250
    mixing_beta = 7.00000e-01,           ! Mixing parameter
/
&IONS
  ion_dynamics = 'bfgs'
/
&CELL
   cell_dofree='all'
   press=0.0
   press_conv_thr= 1d-2
/
CELL_PARAMETERS {angstrom}
  6.712963530000   0.000000000000   0.000000000000
  0.000000000000   6.712963530000   0.000000000000
  0.000000000000   0.000000000000   6.712963530000
ATOMIC_SPECIES
Nb     92.90638  Nb.pbe-spn-rrkjus_psl.1.0.0.UPF
Co     58.933195  Co.pbe-spn-rrkjus_psl.0.3.1.UPF
ATOMIC_POSITIONS {crystal}
Co  0.125000000000   0.125000000000   0.125000000000
Co  0.375000000000   0.375000000000   0.125000000000
Co  0.625000000000   0.625000000000   0.125000000000
Co  0.875000000000   0.875000000000   0.125000000000
Co  0.375000000000   0.125000000000   0.375000000000
Co  0.125000000000   0.375000000000   0.375000000000
Co  0.875000000000   0.625000000000   0.375000000000
Co  0.625000000000   0.875000000000   0.375000000000
Co  0.625000000000   0.125000000000   0.625000000000
Co  0.875000000000   0.375000000000   0.625000000000
Co  0.125000000000   0.625000000000   0.625000000000
Co  0.375000000000   0.875000000000   0.625000000000
Co  0.875000000000   0.125000000000   0.875000000000
Co  0.625000000000   0.375000000000   0.875000000000
Co  0.375000000000   0.625000000000   0.875000000000
Co  0.125000000000   0.875000000000   0.875000000000
Nb  0.500000000000   0.000000000000   0.000000000000
Nb  0.000000000000   0.500000000000   0.000000000000
Nb  0.750000000000   0.250000000000   0.250000000000
Nb  0.250000000000   0.750000000000   0.250000000000
Nb  0.000000000000   0.000000000000   0.500000000000
Nb  0.500000000000   0.500000000000   0.500000000000
Nb  0.250000000000   0.250000000000   0.750000000000
Nb  0.750000000000   0.750000000000   0.750000000000
K_POINTS {automatic}
    6 6 6 0 0 0                  ! Denser Monkhorst-Pack grid for better
accuracy

Thanking you,
SANKHA
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