[gmx-users] energy problems

[Osmany Guirola Cruz]

Hi
 I am doing a simulation of a short peptide in water with counterions Tcoup 
Pcoup ..... but  i do a graph of the total energy and this is the result 

    t(ps)            Potencial        Kinetic                 Total       Temp        
 0.000000  -123848.714738  24317.926256    -99530.788482  303.036540
 0.200000  -128255.528122  26093.377899  -102162.150223  325.161236
 0.400000  -128604.439218  25163.987820  -103440.451398  313.579691
 0.600000  -129228.424209  24885.526342  -104342.897868  310.109658
 0.800000  -129548.890008  24847.294010  -104701.595998  309.633228
 1.000000  -129836.118295  25133.901220  -104702.217076  313.204769
 .............................................
 .......................................
 etc

In the total energy there it's a great jump from the step(0) to the next(0.2) 
similar in the potencial. (after this it oscillate around the averge). is 
this correct? or i have something wrong in my mdp files 
My TCoup=300 but g_energy say that the average is 314 that it's greater than 
the expected value 300. Why?
 
here my mdp file
title               =  fws
cpp                 =  /usr/bin/cpp
constraints         =  all-bonds
integrator          =  md
dt                  =  0.002   
nsteps              =  5000000  
nstcomm             =  1
nstxout             =  5000
nstvout             =  5000
nstfout             =  0
nstlist             =  10
ns_type             =  grid
energygrps          =  Protein  SOL
rlist               =  0.8
;coulombtype            =  PME
rcoulomb            =  1.4
rvdw                =  0.8

; Berendsen temperature coupling is on in three groups
Tcoupl              =  berendsen
tau_t               =  0.1      0.1     0.1
tc_grps             =  protein  sol     CL-
ref_t               =  300      300     300
; Pressure coupling is on
Pcoupl              =  berendsen
pcoupltype          =  isotropic
tau_p               =  0.5
compressibility     =  4.5e-5
ref_p               =  1.0
; Generate velocites is on at 300 K.
gen_vel             =  yes
gen_temp            =  300.0
gen_seed            =  173529