Hi Stefano and Giuseppe,

Thanks for your feedback.

I just wanted to try 48 atom supercell initially and see how it goes (to
save computation time as well). I will try 108 atom supercell definitely.

Is EXX-ACE implemented in QE 6.1v by default or do I have to compile it
separately?. I will try to run it (if our busy HPC facility permits!).

If I am not using HSE , do I have to use LDA level theory for TiO2 with
defects?.

Thanks
Manu
(University of Waterloo)

On Sun, Aug 6, 2017 at 6:08 PM, Giuseppe Mattioli <
giuseppe.matti...@ism.cnr.it> wrote:

>
> On the top of Stefano's answer, I would add that in a 48 atom
> supercell the interaction between the relaxation sphere of an oxygen
> vacancy and its periodic images along the 100 or 010 directions is too
> strong and can lead to an improper description of the electronic
> properties of the defect that can not be considered as an "isolated
> defect" anymore. I suggest that you use at least a 3x3x1 108-atom
> supercell. With the new EXX-ACE implementation you may probably afford
> an HSE calculation, otherwise remember also that the small-polaron
> character of excess electrons in TiO2 such as those induced by the O
> vacancy is not at all well described at the GGA level of theory.
> HTH
> Giuseppe
>
> stefano de gironcoli <degir...@sissa.it> ha scritto:
>
> > yes
> > start from the perfect relaxed geometry (as obtained from vc-relax)
> > remove an atom and relax the internal structure.
> > at the end also perform a vc-relaxation (from the fixed-cell relaxed
> > geometry)
> > stefano
> >
> > On 06/08/2017 17:33, Manu Hegde wrote:
> >> 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 <mailto: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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>     Giuseppe Mattioli
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