[gmx-users] problem going from cut-off to pme

[Mark Abraham]

Yiannis wrote:
> Hello,
> I have a strange problem with a 100 molecule system where I used cut- 
> off electrostatics and I want to use pme from now.
> 
> After md with Coulomb cut-off, I minimised with steep (and the same  
> Coulomb cut-off) and it ends OK:
> 
> I take this minimised .gro and I minimise it again but now I change  to 
> PME electrostatics. It crashes from the beginning with an infinite  
> force (not on the atom with the previous maximum force) and the  energy 
> is huge: 6.56504e+19 instead of -5.0425977e+04 which was the  end of the 
> previous minimisation. Do you have any explanation? Should  I change 
> some PME parameters?

This suggests you are doing something grossly wrong. Check your 
structures visually, check you're actually feeding in the structure you 
think you are, check your .mdp file contains what you think it does.

Mark