[gmx-users] Specific heat calculations using gmx energy

[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*