[gmx-users] Rigid water model

Michelle Aranha maranha at utk.edu
Fri Mar 14 23:00:47 CET 2014

I tried to reproduce results for rigid water with 895 molecules~1000 kg/m3
density, 10 ns NPT simulation (298 K & 1 bar)with Parinello Rahman Barostat
and Berendsen thermostat. Here is my result for SPC water
Kappa (J/m3)	5.689E-10
Cp	22.8054
Cp- Cv	5.94102
The density, diffusion coefficient, the average configuration energy agree
with previous results. However the heat capacity value is quite low as
compared to 75 J/mol K of real water or even that has been previously found
with water models. I compared my values with a 2 ns and 10 ns simulations,
but the heat capacity value shows no real improvement. I do not know much
about quantum corrections hence I have not tried it. Will applying quantum
corrections give the correct heat capacity? 
The isothermal compressibility  reported by GROMACS is in J/m3 and the
adiabatic bulk modulus is reported in m^3/J, could that be a mistake and
should it be rather in  (J/m^3)^-1 and J/m3 respectively. 
And, why does the isothermal compressibility change during the course of
simulation if it has been fixed in the mdp file.

Best wishes,

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