[gmx-users] About energy minimization problem of fatty acids.

[quanta at chem.unipune.ernet.in]

Dear all,
I am new user of GROMACS. I'm triyng to run energy minimization for a
mixture of fatty acid molecules using ffgmx. I have updated ffgmx.rtp,
.hdb and aminoacids.dat files introducing these molecules. The charges are
defined only for the -COOH group and 0.00 for rest of CH2 and CH3 grps.
During energy minimisation I am getting convergence problem as :


Steepest Descents converged to machine precision in 76 steps,
but did not reach the requested Fmax < 1000.
Potential Energy  = -1.60203164239929e+05
Maximum force     =  1.84024599812275e+06 on atom 665
Norm of force     =  5.30962675879254e+06

I am getting same message with conjugate gradient method also.
The resulted geometry shows -OH group to be detached from the residue
molecules.

I have changed the convergence criteria also. But then Potential Energy
results to some high positive number.

Can anyone help me in solving this problem?

Thanks in advance.

Best wishes,

Rashmi