[gpaw-users] Fwd: Charged oxygen vacancy in periodic systems

[Teemu Parviainen]

Hi,
Thank you for this information!

I don't have any experience of generating and manipulating the setups. Also
I have used only paw setups in my earlier calculations so a couple of
questions arises:

-How do you usually fiddle with all the parameters (c_n, v_l, rloc in this
case). I mean is there any basic scheme to change the parameters? What is
the criteria to accept the parameter set?

-Is it OK to mix conventional paw setups with hgh setups (for example
defining hgh setups for Mg and paw for O)?

-How do the results calculated with hgh and paw setups compare with each
other? For example, how do the calculated adsorption energies or vacancy
formation energies compare in general? Has anyone even studied this?

Greetings,
-Teemu Parviainen, PhD student, Jyväskylä Finland




On 13 March 2015 at 12:43, Ask Hjorth Larsen <asklarsen at gmail.com> wrote:

> 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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