Den 2019-07-15 kl. 09:24, skrev Pragati Sharma:
Dear all,
I am simulating a melt of polybutadiene consisting of 60 chains using OPLS
forcefield. After 50 ns of NPT production run, specific heat is calculated
using the command:
*gmx energy -f ener.edr -fluct_props -nmol 60 -driftcorr *
and the value obtained is:
Enthalpy = 2010.04 kJ/mol
Heat capacity at constant pressure *Cp = 22807.5 J/mol K*
However when I calculate Cp from last 5 ns of trajectory the value is:
Enthalpy = 2004.05 kJ/mol
Heat capacity at constant pressure *Cp = 7934.66 J/mol K*
Do the Cp calculation is highly dependent on the equilibration of system or
I am missing something because the experimental valu is ~ 100 *J/mol K, *so
the values from simulation are also high compared to experiments.
*Thanks*
Did you check whether the enthalpy makes a sudden drop in the beginning
of the simulation? If so this will influence the fluctuations a lot.
--
David van der Spoel, Ph.D., Professor of Biology
Head of Department, Cell & Molecular Biology, Uppsala University.
Box 596, SE-75124 Uppsala, Sweden. Phone: +46184714205.
http://www.icm.uu.se
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