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Dear A. Suresh,<br>
<br>
In some cases while relaxing system by vc-relax the relaxed
structure is quite different than starting point structure. <br>
<br>
"The PW basis set used in a variable-cell calculations is determined
by the cutoff and by the <em>initial</em> cell geometry. If you
make a calculation with the <em>final</em> 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."<br>
<br>
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.<br>
<br>
Regards,<br>
K. Gruszka<br>
<br>
<div class="moz-cite-prefix">W dniu 01.06.2016 o 09:26, Suresh A
pisze:<br>
</div>
<blockquote
cite="mid:CAE_UR+WbhPVT0anPRh5sSOONXKOyWBqVnQBRmFoxyQhfUnR7bw@mail.gmail.com"
type="cite">
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<div>Respected Sirs/Friends,<br>
</div>
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.<br>
</div>
For default values:<br>
Total force = 0.000082 Total SCF correction =
0.000002<br>
...................................................<br>
<br>
CELL_PARAMETERS (alat= 6.97686888)<br>
1.016725684 -0.000000000 0.000000000<br>
-0.000000000 1.016725684 0.000000000<br>
0.000000000 0.000000000 2.490647736<br>
<br>
</div>
For Changed parameters:<br>
<br>
The changed parameters are<br>
<br>
&IONS<br>
<br>
ion_dynamics = 'bfgs' ,<br>
trust_radius_max = 0.2D0 ,<br>
trust_radius_min = 0.5D0 ,<br>
trust_radius_ini = 0.1D0 ,<br>
<div><br>
Total force = 0.014421 Total SCF correction =
0.000014<br>
......................................................<br>
<br>
CELL_PARAMETERS (alat= 6.97686888)<br>
1.011136738 0.000000000 0.000000000<br>
0.000000000 1.011136738 0.000000000<br>
0.000000000 0.000000000 2.543455379<br>
<br>
</div>
<div>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.<br>
</div>
Is there any general procedure for doing optimization? If there
please direct me towards the solution.<br>
<div>
<div class="gmail_signature" data-smartmail="gmail_signature">
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With Regards,<br>
</div>
<div style="text-align:right">A.Suresh,<br>
</div>
</div>
<div style="text-align:right">Research Scholar,</div>
</div>
<div style="text-align:right">Madurai Kamaraj
University,<br>
</div>
</div>
<div style="text-align:right">Madurai.<br>
</div>
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