[Pw_forum] vc-relax convergence
Manu Hegde
mhegde at uwaterloo.ca
Mon Aug 7 05:12:34 CEST 2017
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.mattioli at 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 <degironc at 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
> >> <degironc at sissa.it <mailto:degironc at 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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