[Wien] Problem in optimization

[Peter Blaha]

Hard to say anything about the qtl-b, since I do not know your 
structure, your sphere sizes, your rkmax and for which atom/l the 
problems occur.

It is not uncommon that c/a changes drastically with volume, since you 
could have "soft" and "hard" axis, so that whith pressure one axes 
changes much more than another. If you do not find a minimum (but have a 
smooth curve), you need to extend the c/a search.

In all our recent posts (userguide, workshops, ...) it is highly 
recommended to use   run_lapw -min  instead of the old   min_lapw script 
when optimizing internal positions.
In many cases this is much more efficient and stable, although the 
"automatic stopping" of run_lapw -min is still sometimes problematic and 
it takes too long to stop (minimizes positions to forces of 0.5 or below 
gaining only very little energy, although one does request only an 
accuracy of 2 mRy).



On 03/03/2017 03:38 AM, GOUTAM KUMAR GUPTA wrote:
> Dear all
>
> Kindly give your feedback on optimization. I am facing a lot of problem
> of QTLB-error. also as suggested change energy parameter value to take
> care of this error. but the problem is if we change energy parameter
> then comparison of final energy in the scf with different volume or c/a
> ratio become difficult.
>
> kindly suggest any reference on optimization of tetragonal structures
> for both volume and c/a ratio with relaxed atomic positions.
>
>
> Thanks
>
> On Fri, Feb 24, 2017 at 11:04 AM, GOUTAM KUMAR GUPTA
> <pg201381002 at iitj.ac.in <mailto:pg201381002 at iitj.ac.in>> wrote:
>
>     Dear all
>
>     I am trying to optimize tetragonal Cu2ZnSnS4 lattice structure
>     (lattice constant and c/a ratio both). What i did is
>
>     1) first i perform volume optimization at -4, -2,0,2,4 with
>     simultaneous optimization of lattice positions using
>
>     min -I -j "run_lapw -I -fc 1.0 -i 40 "
>
>     in optimize.job script
>
>     my volume optimization run fine and i get minima at 4 % change.
>
>     2) then for each volume i performed c/a ratio optimization at
>     -4,-2,0,2,4 using same command
>
>     min -I -j "run_lapw -I -fc 1.0 -i 40 " in optimize.job file
>
>      Now during my c/a ratio optimization i got minima for 0%, 2% and 4%
>     volume case. but for -4% and -2% volume change i do not get minima
>     and the c/a ratio optimization curve do not show single minima.
>     hence i am facing problem in finding optimized lattice parameters
>     with optimized lattice position. as i an unable to get lowest energy
>     structure.
>
>     2) Some times i see that for 0, 2, 4% volume change optimization
>     runs well but for lower volume change say 1% or 3% it shows QTLB
>     error (keeping all other parameters same). I do not know the exact
>     reason for this.
>
>
>     Kindly give your feedback. If i am doing any wrong in optimization
>     script the kindly suggest modified optimization script for both
>     volume and c/a ratio optimization.
>
>
>     Thanks
>     --
>     *Goutam Kumar Gupta*
>     *Mob:8561995547*
>
>
>
>
> --
> *Goutam Kumar Gupta*
> *Mob:8561995547*
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/TC_Blaha
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