[gmx-users] Large dVpot/dlamda values at lambda = 1

[Sai Kumar Ramadugu]

Hi All,
   I'm trying to run free energy simulations for a linkage change in an
oligosaccharide when bound to its protein.
The linkage changes from beta 1-4 to beta 1-3. I followed the tutorial by
Prof Mobley.
For the lambda values I took 0 to 1 at intervals of 0.05. The values of
dVpot/dlambda from 0.00 to 0.95 seem to be in the range of E3-4. But when I
check the values of dVpot/dlambda for lambda = 1, it goes from E2 to E24 at
the end. This is only for the LBFGS minimization.
Does any one suspect a mistake in my topology or my approach?
Thanks for your time.


Sample .log file of lambda = 1 is pasted below.

           Step           Time         Lambda
            100      100.00000        1.00000

   Energies (kJ/mol)
           Bond          Angle    Proper Dih. Ryckaert-Bell.          LJ-14
    1.06593e+04    8.20816e+03    2.93142e+02    4.26304e+03    8.30759e+03
     Coulomb-14        LJ (SR)  Disper. corr.   Coulomb (SR)   Coul. recip.
    4.13439e+04    1.92653e+05   -1.08257e+04   -1.46637e+06   -2.72128e+05
      Potential Pressure (bar)  dVpot/dlambda  dEkin/dlambda  dG/dl constr.
   -1.48359e+06   -4.15979e+03   -1.01327e+15    0.00000e+00    0.00000e+00

           Step           Time         Lambda
            101      101.00000        1.00000

   Energies (kJ/mol)
           Bond          Angle    Proper Dih. Ryckaert-Bell.          LJ-14
    1.06477e+04    8.21153e+03    2.93330e+02    4.26328e+03    8.31182e+03
     Coulomb-14        LJ (SR)  Disper. corr.   Coulomb (SR)   Coul. recip.
    4.13437e+04    1.92648e+05   -1.08257e+04   -1.49776e+06   -2.72128e+05
      Potential Pressure (bar)  dVpot/dlambda  dEkin/dlambda  dG/dl constr.
   -1.51500e+06   -4.33201e+03   -2.78144e+18    0.00000e+00    0.00000e+00

           Step           Time         Lambda
            103      103.00000        1.00000

   Energies (kJ/mol)
           Bond          Angle    Proper Dih. Ryckaert-Bell.          LJ-14
    1.06776e+04    8.21126e+03    2.93576e+02    4.26328e+03    8.31168e+03
     Coulomb-14        LJ (SR)  Disper. corr.   Coulomb (SR)   Coul. recip.
    4.13437e+04    1.92656e+05   -1.08257e+04   -1.76397e+06   -2.72128e+05
      Potential Pressure (bar)  dVpot/dlambda  dEkin/dlambda  dG/dl constr.
   -1.78117e+06   -5.80136e+03   -1.76071e+24    0.00000e+00    0.00000e+00




Regards
Sai
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