[gmx-users] Schlitters entropy calculation

Bala subramanian bala.biophysics at gmail.com
Fri May 27 18:11:15 CEST 2011

I am a newbie to gromacs, trying to calculate the Schlitters entropy
calculation using the following commands.

g_covar -f  mytraj.xtc  -s  structure.pdb -n index.ndx -b 0 -e 4000 -mwa
g_anaeig -entropy  -temp 300

When i used the above commands, i get the Schlitter entropy value for the
4000 frames, but if i use less than 4000 frames, the program does not
calculate the entropy value and it shows the following result. This happens
irrespective of the region i select from the trajectory or the subset of
atoms i choose for the calculation. I am using gromacs version 4.5.3. I have
the same problem even with previous version of gromacs.

The Entropy due to the Quasi Harmonic approximation is 14895 J/mol K
The Entropy due to the Schlitter formula is nan J/mol K

Any suggestion on what could be going wront.
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