UseConstantRatio between "run"

From: Alessandro Cembran (cembran_at_chem.umn.edu)
Date: Mon Jul 10 2006 - 18:37:38 CDT

Hi all,

I was trying to switch in the same configuration file from a simulation with constant area to one with constant x-y ratio. As indicated at page 15 of the manual one should be able to tune the keywords UseConstantRatio and UseConstantArea between different "run" instructions.Unfortunately I can't get UseConstantRatio to work. This is how my instructions look like:

[All the other Params]
...
UseConstantRatio no
UseConstantArea yes
...
Run $nstep

UseConstantArea no
UseConstantRatio yes
Run $nstep

What happend is that, even if in the output file I get the msgs:
TCL: Setting parameter UseConstantArea to no
TCL: Setting parameter UseConstantRatio to yes
the x-y ratio is not constant anymore. In particular I am using an hexagonal cell and the three PBC vectors should have these proportions:
v1=(R; 0; 0)
v2=(R/2; sqrt(3)*R/2; 0)
v3=(0; 0; h)
Well, looking at the xst file when the second runs start, the ratio of R and {sqrt(3)*R/2} is not correct anymore:

700 79.4796 0 0 39.7398 68.8314 0 0 0 92.6703 0 0 0 4.94171e-05 -1.03457e-05 1.28258e-05 0 0 0
800 79.4796 0 0 39.7398 68.8314 0 0 0 92.7386 0 0 0 3.31655e-05 1.38753e-05 7.9339e-08 0 0 0
900 79.4796 0 0 39.7398 68.8314 0 0 0 92.6086 0 0 0 -3.16706e-05 2.46554e-05 -4.33569e-05 0 0 0
1000 79.4796 0 0 39.7398 68.8314 0 0 0 92.6833 0 0 0 8.40104e-05 7.90624e-05 5.27433e-05 0 0 0
1000 79.4796 0 0 39.7398 68.8314 0 0 0 92.6833 0 0 0 8.40104e-05 7.90624e-05 5.27433e-05 0 0 0
1100 79.7723 0 0 39.8861 69.0286 0 0 0 92.4805 0 0 0 -2.87027e-06 -6.18705e-06 2.81489e-05 0 0 0
1200 79.6904 0 0 39.8452 68.92 0 0 0 92.5743 0 0 0 -3.77328e-05 -3.99561e-05 1.9668e-05 0 0 0
1300 79.726 0 0 39.863 68.9255 0 0 0 92.5869 0 0 0 -1.72041e-06 -3.21073e-06 5.03486e-05 0 0 0

The other way round, if I set UseConstantRatio on and UseConstantArea off from the beginning, the ratio is correct.
I even tried to switch the order ot the tcl commands UseConstantArea/UseConstantRatio with no luck.
This behavior shows up on either altix or linux machines and I am using the pre-built 2.6b1 versions (parallel on altix and serial on linux).

Thanks for the attention,

Alessandro
-- 
Alessandro Cembran,PhD
Post Doctoral Associate
Univ. of Minnesota, Dept. of Chemistry
G2, 139 Smith Hall 207 Pleasant St SE
Minneapolis, MN 55455-0431
Office: +1 612-625-4319
cembran@chem.umn.edu

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