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.
_______________________________________________
Pw_forum mailing list
[email protected]
http://pwscf.org/mailman/listinfo/pw_forum
_______________________________________________
Pw_forum mailing list
[email protected]
http://pwscf.org/mailman/listinfo/pw_forum
