[gmx-users] How to extract extract dV/dlambda data with g_energy??

PeiQuan Chen gromacs at 163.com
Sat May 24 13:08:00 CEST 2003

Dear gmx-users:
  I have done a FEP calculation on the hydration free energy of methanol as been done by Alessandra villa in the JCC 2002(23),548-553.
  I have set ionit_lambda to a distinct number of values(say 21, 0,0.05,0.10 ... 1.0) and
the delta_lambda to 0.0(Method TI).  After MD(200ps) on one points have have done, I use the g_energy program to extract the dv/dlambda from the ener.edr files.
  The command I use is:
  g_energy -f ener.edr -o free.xvg -b 100
  One of the result(lambda=0.1) is the:

Statistics over 50001 steps [ 100.0000 thru 200.0000 ps ], 1 data sets

Energy                      Average       RMSD     Fluct.      Drift  Tot-Drift
dVpot/dlambda               84.7103    64.1511    64.1027  -0.086365   -8.63667  

  Because the dVpot/dlambda is so high(84.7103), and the fluct. is high too(the calucation
hydration free energy value have bone by Alessandra villa is -14.1 KJ/mol). I suspect It been some wrong I have been done. I think it maybe something wrong I have used the g_energy program. Can anyone help me to correct it? 
  Thank you in advance!

Sincerely yours
PeiQuan Chen
PeiQuan Chen 	Department of Chemistry, Nankai University
WeiJin Road 94, TianJin, 300071, P.R.China
phone:	(86)2223506728		Mobile Phone: (+86)13920675030
gromacs at 163.com	

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