[gmx-users] TIP4P and cg ?

Erik Lindahl lindahl at csb.stanford.edu
Wed Feb 18 01:14:01 CET 2004

Hi Weihua,

Water molecules are a bit special since they use "SETTLE" constraints 
and not normal bonds.

The easiest thing is probably to

1. Copy the tip4p.itp file and make a flextip4p.itp (or something)
2. Replace the [ settles ] section with bonds - you can use the same 
parameters as for flexible spc to start with.
3. Edit the topology to include your modified file when FLEXIBLE is 



On Feb 18, 2004, at 12:57 AM, Weihua Guo wrote:

> Hi gmxusers,
>  Does anyone have a "flexible" type of tip4p.itp that I can use for
>  conjugate gradient minimization?
>  My system is a solvated (TIP4P) peptide in opls force field. Using cg 
> to
>  minimize requires the system completely free of constraints. If I use
>  "define = -DFLEXIBLE" it will point to the flexible spc water, which 
> has
>  different number of particles with tip4p and "grompp" won't work.
>  Will the minimization work fine if I just remove the "exclusions" part
>  from the tip4p itp file?
>  Thanks,
>  Weihua Guo
> Weihua Guo
> The University of Chicago
> 5735 S Ellis Ave
> Chicago, IL 60637
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