[Wien] Are fractionally charged atoms possible in Wien2k? / Thank you

[Oleg Rubel]

Dear Stefaan,

thank you very much for the suggestion. I found some mails about 
'insulator in virtual crystal approximation' in 2005 and followed their 
recipe, namely:

- run through inil_lapw using default atomic numbers
- edit nuclear charges in case.struct
- edit corresponding occupancies in case.inst
- edit the total number of electrons in case.in2*
- run SCF circle

The SCF circle converges. It seems that the charge of 0.75 was possible to 
set up. At least the total charge inside unit cell (:CHA label in 
case.scf) corresponds to the expectations. By the way, how can I check 
what the nuclear charge for each atom is and whether it corresponds to the 
value in case.struct?

Thank you once again.


Yours sincerely,

Oleg


On Tue, 12 Feb 2008, Stefaan Cottenier wrote:

>
> What you are doing is identical to the 'virtual crystal approximation'
> -- search the wien2k mailing list archive for this. Shortly said: do a
> normal initialization first, and only afterwards change Z in case.struct
> and case.in2 (not in case.inst). As far as I remember, this can be done
> with 1 digit precision only (x.2, x.3, but not x.25).
>
> Stefaan
>
> Oleg Rubel wrote:
>> Dear Wien2k Users,
>>
>> in calculations of polar semiconductor surfaces, I came to the point where
>> I need to introduce fractionally charged hydrogen atoms in order to
>> passivate an irrelevant side of the slab. The fractionally charged atom
>> means an atom with a non-integer nuclear charge and the corresponding
>> non-integer number of electrons, i.e., 1.25 or 0.75 in the case of
>> fractionally charged hydrogen atoms.
>>
>> My first attempt with WIEN2k_08.1 (Release 14/12/2007) was not successful.
>> I edited the structure file using w2web and put Z=0.75 instead of default
>> 1.0 for hydrogen. In the structure file, I have got 0.8 instead of 0.75,
>> which is a fault of w2web because Z has F5.2 format. Of course it is not
>> what I want, but I decided to stay with 0.8 and continue further. Real
>> problems begin with LSTART. I edited the case.inst file in order to bring
>> the number of electrons in agreement with the nuclear charge Z=0.8. The
>> corresponding part of case.inst is shown below:
>>
>> H 1
>> 1
>> 1,-1,0.7  N
>> 1,-1,0.1  N
>>
>> LSTART stops on 1S orbital of the pseudohydrogen and generates the
>> following error message:
>>
>> ERROR !!! nstop,iter,tets,test 28 1 9.999999939225290E-009
>>
>> If I put the hydrogen charge back to Z=1 and correspondingly change the
>> case.inst file, LSTART runs error free.
>>
>>
>> Any ideas?
>>
>>
>> Thank you in advance,
>>
>> Oleg Rubel
>>
>> ===========================
>> Oleg Rubel, Ph.D.
>> Faculty of Physics
>> Philipps University Marburg
>> Renthof 5, 35032 Marburg, Germany
>> E-mail: Oleg.Rubel at physik.uni-marburg.de
>> Homepage: http://www.staff.uni-marburg.de/~rubel/
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>>
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