[Wien] insulator in virtual crystal approximation

[Peter Blaha]

> I'm using Wien2k and the virtual crystal approximation (VCA) to simulate the
> metallic state in highly Boron doped diamond. K.W. Lee and W.E. Pickett [PRL93
> (2004) 237003] used VCA in the Wien2k code and got a metallic hole Fermi
> surface with a Fermi energy of about 0.8 eV at 2.5 at% doping. When I put 2.5
> at% doping, i.e. I replace Carbon with Z=6 by a virtual atom with Z=5.975, the
> calculation converges into a insulating solution. 

Did you change case.in2 ?? and set the proper number of valence electrons ??
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,....)


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
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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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