[gmx-users] Problems with calculating Cv and Cp

[Lum Nforbi]

Dear all,

      I have run an 8 ns NPT simulation of 2000 molecules of  TIP3P water
and I have a very low Cv value of 12.4748 J/mol K (factor = 0.000164481).
The result is below. I ignored this value and have tried using formulas for
Cv that I found in the two books: Allen and Tildesley & J. M. Haile but I
can't come out with the right answer.
     Has anyone ever calculated Cv or Cp for water manually from scratch and
gotten the right answer? If so, please, could you give me the details of
what you did?

Statistics over 4000001 steps [ 0.0000 thru 8000.0005 ps ], 10 data sets
All averages are exact over 4000001 steps

Energy                      Average       RMSD     Fluct.      Drift
Tot-Drift
------------------------------
-------------------------------------------------
Potential                  -79498.8    285.331    285.331 0.000110205
0.881641
Kinetic En.                 14960.5    191.868    191.854 -0.0010135
-8.10799
Total Energy               -64538.3    353.238    353.232 -0.000903288
-7.22631
Temperature                 299.962    3.84702    3.84673 -2.0321e-05
-0.162568
Pressure (bar)             0.945534    194.613    194.613 0.000164281
1.31425
Box-X                       3.94528 0.00514348 0.00514348
0          0
Box-Y                       3.94528 0.00514348 0.00514348
0          0
Box-Z                       3.94528 0.00514348 0.00514348
0          0
Volume                      61.4097   0.240325    0.24032 6.42593e-07
0.00514075
Density (SI)                  974.3    3.80629    3.80622 -1.04747e-05
-0.0837974
Heat Capacity Cv:      12.4748 J/mol K (factor = 0.000164481)
Isothermal Compressibility: 2.27095e-05 /bar
Adiabatic bulk modulus:        44034.4  bar


Thank you,

Lum
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20091209/011df083/attachment.html>