[Pw_forum] vc-relax convergence
Giuseppe Mattioli
giuseppe.mattioli at ism.cnr.it
Mon Aug 7 00:08:51 CEST 2017
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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>>
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Giuseppe Mattioli
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