[Wien] Question about mBJ calculation

[tran at theochem.tuwien.ac.at]

Dear David,

0.4 is probably large enough such that pseudo-convergence should not
happen. Nevertheless, if you want to be sure that it's ok, you can 
restart the calculation (after having done save_lapw) with the default
mixing parameters in case.inm (MSEC1 with 0.2).

F. Tran

On Sun, 9 Jan 2011, David wrote:

> Professo Blaha,
> 
> Thank you very much for your reply. Since the beginning of my calculation I've
> been taking care of the mixing factor as you recommended. Now the calculation
> seems to be approaching to convergence.
> 
> However I'm a little concerned now about what you call "pseudo-convergence"
> how can I evaluate if my calculation came to a full convergence or a
> pseudo-convergence?
> 
> By the way the mixing factor I'm using right now is 0.4 with the PRATT mixing
> scheme, is this such a small mixing factor that could lead to
> pseudo-convergence?
> 
> Thank you very much for you help Dr. Blaha.
> 
> David Guzman
> Department of Physics
> California State University - Los Angeles
> 
> On 01/09/2011 01:16 AM, Peter Blaha wrote:
> > 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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> >
> 
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