[Wien] Question about mBJ calculation

[David]

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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