[gmx-users] Understanding the results of NVT simulation

[Agnivo Gosai]

Dear Users

I did a NVT simulation with the following key parameters :-

; Temperature coupling
tcoupl      = V-rescale                     ; modified Berendsen thermostat
tc-grps     = DNA_Protein Water_and_ions    ; two coupling groups - more
accurate
tau_t       = 0.1     0.1                     ; time constant, in ps
ref_t       = 300     300                     ; reference temperature, one
for each group, in K

The g_energy outputs for my nvt.edr file are as follows :-

*For Temperature*
Last energy frame read 500 time  100.000

Statistics over 50001 steps [ 0.0000 through 100.0000 ps ], 1 data sets
All statistics are over 10001 points

Energy                      Average   Err.Est.       RMSD  Tot-Drift
------------------------------
-------------------------------------------------
Temperature                 299.638       0.32    4.75446    1.93228  (K)

Question 1 : Is the drift of 1.93 K allowable ??

*For Total Energy*
Last energy frame read 500 time  100.000

Statistics over 50001 steps [ 0.0000 through 100.0000 ps ], 1 data sets
All statistics are over 10001 points

Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Total Energy                -921661        560    8454.34    3197.77
(kJ/mol)

Question 2 : What is the physical significance of a high Err. Est and a
high Tot-Drift ? I am unable to understand if my system is behaving
properly or not.

I use GROMACS 4.5.7 single precision.


Thanks & Regards
Agnivo Gosai
Grad Student, Iowa State University.