[gmx-users] problem with g_energy tool

[Veera Krasnenko]

Dear All,

Could you help me to identify what is going wrong in our calculations
We run g_energy tool with results produced by mdrun (GROMACS).
And we got the follow output:
"...
Statistics over 1500001 steps [ 0.0000 thru 3000.0002 ps ], 5 data sets

Energy                      Average       RMSD     Fluct.      Drift
Tot-Drift  -kT ln<e^(E/kT)>
-------------------------------------------------------------------------------
Potential                   -586133    1715.72    969.946   -1.63418
-4902.54         inf
Kinetic-En.                 46711.9    167.786    167.784 0.000920543
2.76163     47433.7
Total-Energy                -539421    1708.57    958.414   -1.63326
-4899.78         inf
Volume                      359.509    1.36219   0.682818 0.00136104
4.08312     359.985
pV                          23.1223     1475.3     1475.3 0.00232535
6.97605         inf
..."
As you can see many values are calculated as 'infinite'. This
happens because energies produced in previous calculation are about 10^5
kJ. So even e^1000 is pretty big - almost infinite. We tried to
solve this by modifying equation in sources like this:

Before: -kT ln<e^(E/kT)>
After: 1000 * [-kT ln <e^(E/(kT*1000))>]

Now there is no more 'infinities', but we still have doubts
- Is it known problem or this is our problems in calculations on previous
steps or in build ?

Thank you in advance,

Vera