[gmx-users] rigidn or flexible water models

Justin A. Lemkul jalemkul at vt.edu
Mon May 10 13:23:04 CEST 2010

shahab shariati wrote:
> Hi gromacs users
> Is TIP3P water model rigid?

It can be.

> rigidity means deletion of bonded interactions. is it true?

No.  Deletion of bonded interactions means you don't have an intact molecule!

Have a look at the "#ifdef FLEXIBLE" block in the tip3p.itp file.  Flexibility 
simply depends on whether or not the SETTLE algorithm is applied.  A flexible 
water model has a harmonic potential for the H-O-H angle, while a rigid model 
has constrained O-H and H-H distances.


> Thank you so much for any help!


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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