[gmx-users] Different temperature

[Andrea Carotti]

Hi all,
sorry for the long message.
I'm performing an MD on a system made by a protein and water. I use the 
gromos96 ff.
In the mdp section I've specified this
; Berendsen temperature coupling is on in two groups
Tcoupl              =  Berendsen
tc-grps             =  Protein  SOL
tau_t               =  0.5      0.5
ref_t               =  300      300
; Energy monitoring
energygrps          =  Protein  SOL
; Isotropic pressure coupling is now on
Pcoupl              =  Berendsen
Pcoupltype          =  isotropic
tau_p               =  0.5
compressibility     =  4.5e-5
ref_p               =  1.0

Now, the MD goes without problems but checking the md0.log (i'm using two 
processor (-np 2 flag)) I've found something corious:
       Step           Time         Lambda
              0        0.00000        0.00000
--
    Kinetic En.   Total Energy    Temperature Pressure (bar)
    1.01748e+05   -4.20959e+05    3.03213e+02    7.26556e+00
--
           Step           Time         Lambda
           5000       10.00000        0.00000
--
    Kinetic En.   Total Energy    Temperature Pressure (bar)
    1.17913e+05   -4.04404e+05    3.51387e+02   -5.96647e+01
--
           Step           Time         Lambda
          10000       20.00000        0.00000
--
    Kinetic En.   Total Energy    Temperature Pressure (bar)
    1.17628e+05   -4.03422e+05    3.50536e+02   -3.19202e+01
--
           Step           Time         Lambda
          15000       30.00000        0.00000
--
    Kinetic En.   Total Energy    Temperature Pressure (bar)
    1.16931e+05   -4.04766e+05    3.48458e+02    2.64246e+02
--
           Step           Time         Lambda
          20000       40.00000        0.00000
--
    Kinetic En.   Total Energy    Temperature Pressure (bar)
    1.17938e+05   -4.04368e+05    3.51460e+02    1.27911e+01
--
           Step           Time         Lambda
          25000       50.00000        0.00000
--
    Kinetic En.   Total Energy    Temperature Pressure (bar)
    1.17543e+05   -4.06008e+05    3.50284e+02   -1.53993e+02

As you can see the temperature increase rapidly to a value near 350K. Could 
you please explain me the problem (if it's a problem) and point me out some 
suggestions to solve it?
Thanks in advance
Andrea