Look up the SPC-Fw paper by Yujie Wu. The angle constant, which is
probably tuned to get bulk properties just like everything else, would be
interdependent on the charges and vdW parameters. If you want to fit an
angle parameter to reproduce specific quantum data, use mdgx and see what
comes out. Another thing to point out for avid readers is that TIP3P and
other rigid models have a bond between the hydrogens to enforce their
geometry.
On Wed, Apr 4, 2018 at 8:22 PM, pengfei li <ldsoar1990.gmail.com> wrote:
> Hi Carlos and Dave,
>
> That is a good point. It seems it doesn’t matter when using SHAKE since it
> is rigid.
> I am just curious if SHAKE was not used, is 50.0 kcal/(mol*Rad^2) a better
> choice
> than 100.0 kcal/(mol*Rad^2)?
>
> Best regards,
> Pengfei
>
> > On Apr 5, 2018, at 8:20 AM, David Cerutti <dscerutti.gmail.com> wrote:
> >
> > I'm in agreement with Carlos--the force constants for rigid water models
> > are placeholders. For SPC-Fw, the angle constant does matter, but
> > understand it's essentially making a fixed charge water model
> polarizable,
> > in a sense.
> >
> > On Wed, Apr 4, 2018 at 8:17 PM, Carlos Simmerling <
> > carlos.simmerling.gmail.com> wrote:
> >
> >> Since the water is rigid and there is a bond between the H atoms, does
> the
> >> force constant matter?
> >>
> >> On Wed, Apr 4, 2018, 8:14 PM pengfei li <ldsoar1990.gmail.com> wrote:
> >>
> >>> Hi Everyone,
> >>>
> >>> Does anybody know how does the force constant for HW-OW-HW angle come
> >>> from? I found it is 100.0 kcal/(mol*Rad^2) but 50.0 kcal/(mol*Rad^2)
> is a
> >>> more reasonable choice based on Hessian matrix of B3LYP/6-31G* level of
> >>> calculations. However, I could not find a value in the original
> >> TIP3P/TIP4P
> >>> article (Jorgensen, W. L.; Chandrasekhar, J.; Madura, J. D.; Impey, R.
> >> W.;
> >>> Klein, M. L. J. Chem. Phys. 1983, 79, 926-935.). So I am just curious
> >> about
> >>> what does the original value come from? Thanks!
> >>>
> >>> Best regards,
> >>> Pengfei
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Received on Wed Apr 04 2018 - 17:30:05 PDT
