[Pw_forum] Relaxed Structure: Reg

[Konrad Gruszka]

Dear A. Suresh,

In some cases while relaxing system by vc-relax the relaxed structure is 
quite different than starting point structure.

"The PW basis set used in a variable-cell calculations is determined by 
the cutoff and by the /initial/ cell geometry. If you make a calculation 
with the /final/ geometry at the same cutoff, you get slightly different 
results because the PW basis set is different. The difference should be 
small, though, unless you are using a too low cutoff for your system. 
Since v.4.3.1, a final scf step is performed at the end of the vc-relax 
run, with the PW basis set computed for the final geometry, to check for 
this."

So, when your final structure is very different from starting one, you 
should again relax your system, and parameters obtained from last relax 
procedure should be used further.

Regards,
K. Gruszka

W dniu 01.06.2016 o 09:26, Suresh A pisze:
> Respected Sirs/Friends,
>                                 I have optimised the anatase 
> structure(vc-relax) by default bfgs controlling parameters and with 
> changed  controlling parameters. Now I got two different lattice 
> parameters and forces as shown below.
> For default values:
> Total force =     0.000082     Total SCF correction = 0.000002
> ...................................................
>
> CELL_PARAMETERS (alat=  6.97686888)
>    1.016725684  -0.000000000   0.000000000
>   -0.000000000   1.016725684   0.000000000
>    0.000000000   0.000000000   2.490647736
>
> For Changed parameters:
>
> The changed parameters are
>
>  &IONS
>
>             ion_dynamics = 'bfgs' ,
>             trust_radius_max = 0.2D0 ,
>             trust_radius_min = 0.5D0 ,
>             trust_radius_ini = 0.1D0 ,
>
> Total force =     0.014421     Total SCF correction = 0.000014
> ......................................................
>
> CELL_PARAMETERS (alat=  6.97686888)
>    1.011136738   0.000000000   0.000000000
>    0.000000000   1.011136738   0.000000000
>    0.000000000   0.000000000   2.543455379
>
> Which Lattice parameters I have to take for further calculations? And 
> there is a big difference in final force value for the structure where 
> bfgs controlling parameters are changed. In the input file I actually 
> given high convergence thresold value (conv_thr = 1.D-8) and default 
> forc_convr_thr values.
> Is there any general procedure for doing optimization? If there please 
> direct me towards the solution.
> With Regards,
> A.Suresh,
> Research Scholar,
> Madurai Kamaraj University,
> Madurai.
>
>
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