[gmx-users] Step size too small

[Sheyore Omovie]

Dear gmx-users,
 
I have 2 molecules in a box, as usual pdb2gmx saw them as one. i edited the .top file to remove the bonds created between the two molecules, I also added a distance restraint btw the molecules. (The 2 structures have been separately minimized). However, I get the ff message for EM run:
Stepsize too small, or no change in energy.
Converged to machine precision,
but not to the requested precision Fmax < 1000
 
Double precision normally gives you higher accuracy.
 
Steepest Descents converged to machine precision in 15 steps,
but did not reach the requested Fmax < 1000.
Potential Energy  =  1.0246325e+20
Maximum force     =            inf on atom 1
Norm of force     =            inf
I would appreciate any advice on how to fix this.
Rgds
John
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