[Wien] Re: insulator in virtual crystal approximation

[Moritz Hoesch]

Dear Peter,

> Did you change case.in2 ?? and set the proper number of valence  
> electrons ??
No I didn't!! Thank you for the instruction. Now I could reproduce  
the result.

To recap: I have to change the values (1) in the case.struct file  
[per atom] (2) in the case.inst file [per atom] and (3) in the  
case.in2 file [per unit cell].

A word of caution: the w2web struct-generator doesn't like virtual  
atoms and will change them to real integer charge atoms. I edited the  
case.struct file by hand.


> You should have a non-integer number and thus you MUST get a metallic
> solution.
> (How do you determine you are metallic or insulating ? k-mesh ?  
> "shifted
> k-mesh problem,....)
I calculate either the DOS or the spaghetti around the Gamma point  
(valence band maximum) and look at the position of the Fermi level.  
With the charge of 7.95 [per unit cell] in case.in2 I get the  
metallic band now. Thanks again.

I checked carefully that the "test of charge neutrality" in  
case.outputd gives a consisten result [11.95 electrons per unit cell]  
but this was obviously the wrong place to look.

Moritz



>> At 2.9% and above I get a
>> metallic band structure with E_F of about 1 eV, i.e. the Fermi  
>> level is about
>> 1 eV below the (now unoccupied) valence band maximum. I don't do  
>> any phonons
>> (yet) like Lee and Pickett did, I just want to get the ground  
>> state of the
>> undistorted lattice. I tried volume optimization and found a 4%  
>> volume
>> expansion, but at 2.5% doping I get an insulating state for all  
>> lattice
>> parameters.
>>
>> How can I reproduce the result of Lee and Pickett? Is there a  
>> trick for VCA?
>> Where do my 0.025 electrons per atom go? Or is this some kind of Mott
>> transition in the GGA?
>>
>> I use GGA with the 1s as core electron (energy separation -6 Ry).  
>> To sample
>> the small Fermi surface well I use a dense k-mesh of 1240 k-points  
>> in the
>> reduced wedge (36 x 36 x 36 in total). I use WIEN2k_05.3 (Release  
>> 3/4/2005)
>> and I got the same result also with Wien97. I attach my .struct  
>> and .inst file
>> to this e-mail.
>>
>> Many thanks for any elucidating remarks
>>
>> Moritz
>>
>> ??
>>
>>
>>
>> -------------
>> Moritz Hoesch
>> JSPS Postdoctoral Research Fellow
>>
>> Synchrotron Radiation Research Center                phone   
>> +81-791-58-2643
>> (PHS 3808)
>> Japan Atomic Energy Research Institute (JAERI)        fax    
>> +81-791-58-2740
>>
>> 1-1-1 Koto, Mikazuki-cho, Sayo-gun
>> Hyogo 679-5148 JAPAN
>>
>>
>>
>
>
>                                       P.Blaha
> ---------------------------------------------------------------------- 
> ----
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
> Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/ 
> theochem/
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