[gpaw-users] Charged oxygen vacancy in periodic systems

[Ask Hjorth Larsen]

Hello

Setups are extremely complicated, so if you fiddle with them it'll
probably just result in garbage.  The HGH pseudopotentials are simple;
you can create your own, providing/hacking a humane number of
parameters.

Grab the objects that encode the minimal set of parameters to specify
the setup, and then improvise from there changing number of valence
electrons, etc.:

>>> from gpaw.hgh import setups
>>> setups['Si']
<gpaw.hgh.HGHParameterSet instance at 0x8cf798c>
>>> dir(setups['Si'])
['Nv', 'Z', '__doc__', '__init__', '__module__', '__str__', 'c_n',
'configuration', 'copy', 'get_occupation_numbers', 'nl_iter',
'print_info', 'rloc', 'serialize', 'symbol', 'v_l', 'zeropad']

Nv is valence electron number, c_n are coefficients, and v_l is a list
of VNonLocal objects with info on the atomic Hamiltonian
contributions.  Mix them however you like them and create a
HGHParameterSet with that.  Then instantiate a HGHSetupData from that,
and run your calculations with GPAW(setups={17: my_hghsetupdata}) to
specify a custom setup for atom 17.

Best regards
Ask


2015-03-13 7:53 GMT+01:00 Ioannis Remediakis <remed at materials.uoc.gr>:
> On 11/03/2015 09:15, Teemu Parviainen wrote:
>>
>> Hi all,
>> I want to do calculations for charged oxygen vacancies in periodic
>> systems (MgO surface). Does anyone have any experience what is the best
>> way to do this with gpaw? I came across to a method called Virtual
>> Crystal Approximation and if I understood correctly I have to change the
>> nuclear number of all Mg atoms so that the overall change corresponds to
>> the charge of the vacancy. Is this correct? How is this done in gpaw? Is
>> it sufficient to just change the Z number in the PAW setup file or do I
>> need to generate completely new one?
>>
>> Thanks in advance,
>>
>> -Teemu Parviainen, PhD student, Jyväskylä Finland
>>
>> --
>
>
>
> Dear all,
>
> I would like to ask a more general question: is it possible to use VCA
> (virtual crystal approximation) in GPAW?
>
> This method is very efficient in alloys of atoms with similar sizes and same
> number of valence electrons, such as SiGe. Instead of using a large cell
> with Si and Ge atoms, you use a small cell with virtual "SiGe" atoms.
>
> VCA is implemented in some codes, such as Espresso. If I understand
> correctly, the pseudopotential for the virtual atom is the average of the
> two pseudopotentials. But I do not know how one could do this in GPAW.
>
> Any help would be appreciated. Thank you!
>
> best regards,
> Ioannis
>
>
> --
> ----------------------------------------------
> Ioannis N. Remediakis
> Department of Materials Science and Technology
> University Of Crete,  710 03 Heraklion, Greece
> Tel: +30 2810 394250      Fax: +30 2810 394201
>                 http://theory.materials.uoc.gr
> ----------------------------------------------
>
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