Hello Stephano,
Thanks for your reply. Just to double check what you meant before starting
the calculations, you mean take the equilibrium values from the vc-relax
calculation (perfect cell,  only co-ordinates) and do the 'relax'
calculation with defect?.
Manu
(University of Waterloo).


On Sun, Aug 6, 2017 at 11:15 AM, stefano de gironcoli <degir...@sissa.it>
wrote:

> does the energy (enthalpy) decreases as the vc-relaxation progresses ?
> The local structure around the defect may be quite different. It may just
> take long.
>
> I would start by performing a fixed cell relaxation with the cell
> parameters fixed at the undefected equilibrium values. And only after that
> I would start the vc-relax calculation from the so relaxed configuration to
> evaluate the vacancy formation volume. The local arrangement around the
> defect should be already more or less ok (if the supercell is large
> enough).
>
> HTH
> stefano
>
>
>
> On 06/08/2017 16:40, Manu Hegde wrote:
>
> Hello,
>
> I am trying to optimize anatase TiO2 supercell with 48 atoms. The
> supercell converges in 15 BFGS cycles for a perfect cell. But when I
> introduce defect (by removing one of the oxygen atom), the vc-relax is not
> t all converging. I am using the same parameters in both the cases. Can
> anyone give some feedback on this.?.  Here is my input,
>
>
> &control
>                  calculation = 'vc-relax' ,
>                 restart_mode = 'from_scratch' ,
>                       outdir = '/work/mhegde/tmp_tiodef/',
>                   pseudo_dir = '/home/mhegde/tio_project/def_tio/',
>                       prefix = 'tioan',
>                    verbosity = 'high',
>
>  /
>  &system
>                        ibrav = 0,
>                        nat = 47,
>                         ntyp = 2,
>                      ecutwfc =40,
>                      ecutrho=400,
>                      occupations='smearing',
>                       degauss=0.003
>
>  /
>  &electrons
>                     conv_thr = 1.D-6,
>                     mixing_beta=0.1
> /
> &ions
>                     ion_dynamics='bfgs'
>
> /
> &cell
>                     cell_dynamics='bfgs'
>
> /
> ATOMIC_SPECIES
>    Ti  47.867000  Ti.pw91-nsp-van.UPF
>    O   15.99900   O.pw91-van_ak.UPF
>
> ATOMIC_POSITIONS angstrom
> Ti       0.00000000       2.84182500       1.20970000
> Ti       1.89455000       2.84182500       3.62910000
> O        0.00000000       0.94727500       1.99939216
> O        0.00000000       2.84182500       4.41879216
> O        1.89455000       0.94727500       2.83940784
> Ti      -1.89455000       0.94727500      -3.62910000
> Ti       0.00000000       0.94727500      -1.20970000
> O       -1.89455000      -0.94727500      -2.83940784
> O       -1.89455000       0.94727500      -0.42000784
> O        0.00000000      -0.94727500      -1.99939216
> O        0.00000000       0.94727500      -4.41879216
> Ti       0.00000000      -0.94727500       1.20970000
> Ti       1.89455000      -0.94727500       3.62910000
> O        0.00000000      -2.84182500       1.99939216
> O        0.00000000      -0.94727500       4.41879216
> O        1.89455000      -2.84182500       2.83940784
> O        1.89455000      -0.94727500       0.42000784
> Ti      -1.89455000      -2.84182500      -3.62910000
> Ti       0.00000000      -2.84182500      -1.20970000
> O       -1.89455000       2.84182500      -2.83940784
> O       -1.89455000      -2.84182500      -0.42000784
> O        0.00000000       2.84182500      -1.99939216
> O        0.00000000      -2.84182500      -4.41879216
> Ti      -3.78910000       2.84182500       1.20970000
> Ti      -1.89455000       2.84182500       3.62910000
> O       -3.78910000       0.94727500       1.99939216
> O       -3.78910000       2.84182500       4.41879216
> O       -1.89455000       0.94727500       2.83940784
> O       -1.89455000       2.84182500       0.42000784
> Ti       1.89455000       0.94727500      -3.62910000
> Ti      -3.78910000       0.94727500      -1.20970000
> O        1.89455000      -0.94727500      -2.83940784
> O        1.89455000       0.94727500      -0.42000784
> O       -3.78910000      -0.94727500      -1.99939216
> O       -3.78910000       0.94727500      -4.41879216
> Ti      -3.78910000      -0.94727500       1.20970000
> Ti      -1.89455000      -0.94727500       3.62910000
> O       -3.78910000      -2.84182500       1.99939216
> O       -3.78910000      -0.94727500       4.41879216
> O       -1.89455000      -2.84182500       2.83940784
> O       -1.89455000      -0.94727500       0.42000784
> Ti       1.89455000      -2.84182500      -3.62910000
> Ti      -3.78910000      -2.84182500      -1.20970000
> O        1.89455000       2.84182500      -2.83940784
> O        1.89455000      -2.84182500      -0.42000784
> O       -3.78910000       2.84182500      -1.99939216
> O       -3.78910000      -2.84182500      -4.41879216
>
> K_POINTS {automatic}
>
>  2 2 2   0 0 0
>
> CELL_PARAMETERS angstrom
>
>  7.57820000       0.00000000       0.00000000
>  0.00000000       7.57820000       0.00000000
>  0.00000000       0.00000000       9.67760000
>
> Thanks,
> Manu
> (University of Waterloo)
>
>
>
>
>
>
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