[gmx-users] energy minimisation of Si3N4 did not converge

Kothai Thiruvengadam tkothai11 at gmail.com
Mon Jan 25 11:22:13 CET 2010

Dear all,
I am using MD simulation of a protein on Silicon nitride surface. The
surface has been created using VMD and tcl script (ref. bionano
tutorial).The protein+surface complex also has been generated using
VMD.Using that PDB file I have done md simulation in gromacs. One itp file
for silicon nitride has been developed using PRODRG server and included in
the top file.
But, during energy minimisation  I got a message
Steepest Descents did not converge to Fmax < 8000 in 2001 steps.
Potential Energy  = -4.5347610e+06
Maximum force     =  1.0913173e+05 on atom 7417
Norm of force     =  2.8918979e+02

The EM ends without converging to Fmax. I put different  values of Fmax and
steps starts from 1000. But for  Fmax 8000 and  2000 steps also I am getting
the same message. What force field I can use for Silicon nitride surface?
How can I rectify this error?
- T.Kothai
Centre for Biotechnology
Anna University Chennai
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