[gmx-users] g_dos to calculate the heat capacity from a simulation of TIP4P water

[Sal Lim]

Hello,

I would like to use g_dos to calculate the heat capacity from a simulation
of liquid TIP4P water. I ran an NVT simulation with around 5000 molecules
for 100 ps (after equilibrating for several ns in NPT), with a time step of
0.0002 ps at 298 K (the *mdp file I used is very similar to that posted by
Caleman et al.'s supplementary material for their DOS simulations, in case
someone is familiar with that work [Caleman et al, J. Chem. Theory Comput,
2012, 8 61]) I save the data every 4 fs.  The velocity autocorrelation
function has.

>From g_dos I find the heat capacity is around 39 J/mol K, but I was
expecting about twice that (around 80 J/mol K). Is there something I need
to include when running g_dos, aside from specifying the relevant
temperature and files (*trr and *tpr)?


I am using GROMACS 4.6.2.

Any suggestions would be greatly appreciated.