[gmx-users] combining energy files

[nishap.patel at utoronto.ca]

Hello,

    I am a running a simulation of 100ns, so I have two edr files  
md.edr and md.part0002.edr. When I calculate some of the energy values  
using g_energy for each of the .edr files individually I get the  
following result:
For md.edr:
Statistics over 27120401 steps [ 0.0000 thru 54240.8008 ps ], 4 data sets
All averages are over 271205 frames

Energy                      Average       RMSD     Fluct.      Drift   
Tot-Drift
-------------------------------------------------------------------------------
Temperature                 297.996    3.75973    3.75972 6.88223e-07   
0.0373298
Pressure (bar)              1.66199    262.287    262.287 -2.24459e-05  
   -1.21748
Volume                      66.1617    0.39728    0.39728          0    
        0
Density (SI)                983.924    5.90292    5.90292 -1.44217e-07  
-0.00782243
Heat Capacity Cv:      12.4747 J/mol K (factor = 0.000159181)
Isothermal Compressibility: 5.79816e-05 /bar
Adiabatic bulk modulus:        17246.9  bar

For md.part0002.edr
Statistics over 22986601 steps [ 54026.8008 thru 100000.0078 ps ], 4 data sets
All averages are over 229867 frames

Energy                      Average       RMSD     Fluct.      Drift   
Tot-Drift
-------------------------------------------------------------------------------
Temperature                 297.993    3.75398    3.75397 -5.66217e-07  
-0.0260308
Pressure (bar)              1.51511    263.692    263.692 4.88234e-05   
   2.24457
Volume                      66.1617   0.398494    0.39849 1.29794e-07  
0.00596703
Density (SI)                983.924     5.9329    5.93284 -1.92684e-06  
  -0.088583
Heat Capacity Cv:      12.4747 J/mol K (factor = 0.000158697)
Isothermal Compressibility: 5.8337e-05 /bar
Adiabatic bulk modulus:        17141.8  bar

But then when I combined my .edr files using eneconv -f md.edr  
md.part002.edr. the output is saved into 'fixed.edr' and when I ran  
fixed.edr file through g_energy, I get negative values as follows :
Statistics over 50000001 steps [ 0.0000 thru 100000.0078 ps ], 4 data sets
All averages are exact over 50000001 steps

Energy                      Average       RMSD     Fluct.      Drift   
Tot-Drift
-------------------------------------------------------------------------------
Temperature              -5.90251e-06          0          0          0  
          0
Pressure (bar)           4.46175e-06          0          0  
-9.66961e-07 -0.0966961
Volume                   -1.32585e-06          0          0          0  
          0
Density (SI)             -1.96389e-05          0          0 -2.119e-07  
   -0.02119
Heat Capacity Cv:      12.4718 J/mol K (factor = 0)
Isothermal Compressibility:          0 /bar
Adiabatic bulk modulus:            inf  bar

I don't understand what happened there. Could someone please help me  
understand if I am combining the files correctly, or it is something I  
am missing.

Thanks

Nisha Patel