[Wien] Question about mBJ calculation

[Peter Blaha]

Convergence of mBJ calculations is sometimes a bit tricky since not only 
the charge density but also the kinitic energy density (or the 
"vresp"-files) determine the potential.

The recommended way is to start out with a PRATT mixing (with eg. 0.2)
and once the :DIS has settled a bit (decreased from the initially big
values, but then not changing much, usually after ~10 iterations) one 
can graduadely increase the mixing factor (to eg. 0.3 and 0.4). Maybe 
:DIS increases a little, but as long as there are no oszillations in 
:ENE or :GAP this is fine.
Eventually, one may intermediately "save" the calculations (to have a 
restarting point) and continue with MSEC1, since once the vresp-files 
are partially converged, density-mixing as done with MSEC1 should be fine.
Please be aware, that in mBJ-calculations not only the density (clmsum) 
is mixed, but that the mixing-factor in case.inm also mixes the 
exchange-potential in lapw0. Thus, there is a danger of 
"pseudo-convergence" when the mixing factor is too small.

Am 09.01.2011 00:31, schrieb David:
> Dear Professor Blaha and Wien users,
>
> I'm running mBJ calculations for CuZrTiO5, spin-polarized, it has 16
> atoms in the unit cell, and im running 300 k-points. My ultimate goal is
> to get the band structure of this crystal.
>
> I haven't got any problems regarding code errors, in fact up to now
> everything has run very smooth. My question though is the following: the
> has has run 58 cycles now and the charge distance does not seem to
> reduce significantly, in fact for the first 45 cycles or so it reduced
> very slow, but now it's going up again, I was wondering if this is a
> common behaviour? Also I was wondering if there is any way I can make it
> converge faster, I know this is a large calculation, but may be some of
> you guys have suggestions.
>
> Some details about my calculation:
>
> 1. I run a regular spin-polarized scf cycle using the MSEC1 with a
> mixing factor of 0.2 and it converged in 18 cycles (convergence criteria
> was charge: 0.00001 e)
>
> 2. I followed the steps for mBJ calculations from the manual, I used
> PRATT with a mixing factor of 0.2 and the convergence criteria is
> charge: 0.00001 e
>
> 3. Attached are the case.struct and case.inst if it helps
>
> Please if you required any other information in order for me to get some
> help, I can send it
>
> Thank you very much
>
> David Guzman
> Department of Physics
> California State University - Los Angeles
>
>
>
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-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671