[Wien] equivalent-core approximation

[Michael Gurnett]

Thank you Peter for your very indepth reply. This method you have is what I 
originally tried. Howerver, once I made all the changes I found that the SCF 
would oscilate even with a mixing factor of 0.01 and would eventually crash. 
If this is the best method I will try it again, and with any luck I can 
continue on from there.

Once again thank you for your answer.

Michael



----- Original Message ----- 
From: "Peter Blaha" <pblaha at zeus.theochem.tuwien.ac.at>
To: <wien at zeus.theochem.tuwien.ac.at>
Sent: Thursday, February 24, 2005 3:50 PM
Subject: Re: [Wien] equivalent-core approximation


> I'm not an expert in these core level calculations, but for me the z+1
> approximation always seemed a quite poor approximation and I would not use
> it if I have another chance.
>
> For your problem I propose two methods within WIEN:
>
> First of all you should always have a supercell (unless you have a big 
> cell
> anyway) with broken symmetry so that you can deal with a core hole on a
> single Ge atom (screened by the environment).
> In addition, try to make the Ge sphere "as large" as possible (but still
> meaningfull - details depend on your structure).
>
> Firt do a regular WIEN calculation for this supercell to verify that you 
> get
> identical results as before.
>
> Then you have to do some tricks:
>
> Edit case.inc and put the Ge 3d electrons into the core for  all Ge atoms
> (I'm not sure about this, but I guess it is more cosistent than just for
> the single Ge atom) ?
>
> edit case.in2(c) and reduce NE by 10*(number of Ge atoms)
>
> edit case.in1(c) (make a backup first) and remove the Ge-3d LO
> (around -1.5 Ry). Do not forget to
> change also the "number of exceptions" (see UG description of case.in1)
>
> Do an scf calculation. Check the results, i.e. core-leakage and the effect
> on the Ge-3d eigenvalues (compare the 3d core with the 3d bands with 
> respect
> to EF). Of course the bands will have a certain bandwidth which is not
> present in the core (but there you have SO splitting).
>
> Once you can estimate the "error" introduced by the core-like treatment 
> you may
> remove 1 or 1/2 core electron from case.inc and add it to case.in2. Do 
> another
> scf calculation and estimate your core levels (E-tot or Slater...).
>
> At this position, your 3d-core with the hole should be quite separated 
> from
> the other Ge. You could now try a "2-window calculation" using a case.in2s
> file.
> Remove all 3d states from the inc file.
> Take the original case.in1 file (so that you have again 3d LOs)
> cp case.in2 case.in2s
> edit case.in2s and specify NE=9 (just for the Ge 3d with hole)
> edit case.in2 with NE="all electrons+1"; but set EMIN such that the 
> 3d-states
> of the Ge-hole atoms are cut-off.
> cp case.in1 case.in1s
>
> Finally you will have to edit   run_lapw
> Look for     lapw1s:
> replace the line
>     total exec lapw1 -sc $para
> by   cp $file.vector $file.vectors
>
> Now run an scf cycle. You should have the Ge-3d states in the valence, but
> have introduced a hole in the Ge-3d states of one particular atom.
>
> It's not simple and maybe I've made an error in the description, but I'd
> expect it should work. (Of course, if the core leakage is not that bad
> you might not need the second step).
>
>
>
>
>> Ge 3d electrons (approx. -1.5 ryd). So far I have tried manually placing 
>> these
>> in core and reducing the number of valence electrons. However, this too 
>> was
>> unstable. Another method I have heard about is simply using the Slater
>
> What should that mean ? I'm pretty sure it works.
>
>
>                                      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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