[QE-users] Why is my VC-RELAX not showing converged result?

[Naharin Jannath]

I ran the VC-RELAX for simple niobium until I get a converged value. But at
the bottom of the output, the cell parameter stops changing. Also, the
pressure is well below the "pres_conv_thr" which was set to 0.01 in the
input file. Can anyone tell me how to fix it? Also, my CELL_PARAMETER vs K
curve is not smooth even using large smearing.
&CONTROL
calculation = 'vc-relax'
restart_mode = 'from_scratch'
prefix = 'Nb'
etot_conv_thr = 0.000001
pseudo_dir = '.'
outdir = '.'
disk_io = 'none'
tstress = .true.
tprnfor = .true.
/
&SYSTEM
degauss = 0.05
ecutrho = 360
ecutwfc = 45
ibrav = 0
nat = 1
ntyp = 1
occupations = "smearing"
smearing = "gaussian"
/
&ELECTRONS
conv_thr = 1.0e-08
electron_maxstep = 200
mixing_mode = 'plain'
mixing_beta = 0.5
startingpot = "atomic"
startingwfc = "atomic+random"
/
&IONS
ion_dynamics = "bfgs"
/
&CELL
cell_dynamics = "bfgs"
press_conv_thr = 0.01
/
ATOMIC_SPECIES
Nb 92.90638 Nb.pbe-spn-kjpaw_psl.0.3.0.UPF
ATOMIC_POSITIONS {crystal}
Nb 0.00 0.00 0.00
CELL_PARAMETERS {angstrom}
1.675751271 1.675751271 1.675751271
-1.675751271 1.675751271 1.675751271
-1.675751271 -1.675751271 1.675751271
K_POINTS {automatic}
10 10 10 0 0 0
output --
PRESSURE -
total stress (Ry/bohr**3) (kbar) P= -47.02
total stress (Ry/bohr**3) (kbar) P= -9.58
total stress (Ry/bohr**3) (kbar) P= 0.65
total stress (Ry/bohr**3) (kbar) P= 0.02
total stress (Ry/bohr**3) (kbar) P= 0.01
total stress (Ry/bohr**3) (kbar) P= -0.21
CELL_PARAMETERS (angstrom)
1.662361144 1.662361144 1.662361144
--
CELL_PARAMETERS (angstrom)
1.659001159 1.659001159 1.659001159
--
CELL_PARAMETERS (angstrom)
1.659212618 1.659212618 1.659212618
--
CELL_PARAMETERS (angstrom)
1.659217666 1.659217666 1.659217666
--
CELL_PARAMETERS (angstrom)
1.659217666 1.659217666 1.659217666
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