[gmx-users] hydration free energy

[dgfd dgdfg]

Hi. I have calculated deltaG of hydration for my molecule in 101 steps. First 50 steps I decoupled coulomb interactions and last 50 - vdw. After all I calculated resulting value by the command
gmx bar -f {0..100}/dhdl.xvg -o -oi -oh -b 500 >RESULT
and found such phrase in the output

Temperature: 300 K
Detailed results in kT (see help for explanation):
 lam_A  lam_B      DG   +/-     s_A   +/-     s_B   +/-   stdev   +/- 
     0      1    8.16  0.11    0.34  0.06    0.34  0.06    0.91  0.02
     1      2    7.61  0.07    0.21  0.08    0.19  0.07    0.86  0.01
...
...
...
    97     98   -0.40  0.02    0.42  0.02    0.55  0.02    0.97  0.01
    98     99   -2.11  0.03    1.16  0.03    1.84  0.06    1.75  0.03
    99    100  -17.55  0.43   13.60  0.44 62204236256674537472.00 33302891096617504768.00  102.60 10.21
WARNING: Some of these results violate the Second Law of Thermodynamics: 
         This is can be the result of severe undersampling, or (more likely)
         there is something wrong with the simulations.

Please answer what is wrong in my simple algorythm. It is based on tutorial  http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin/gmx-tutorials/free_energy/index.html with some simplification. All necessary data attached.

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