Hi Vlad,
The reason is probably because of the timing involved in releasing the
force field sets.
The JC parameters were published before the OPC model, so in publishing
their OPC water model the authors used the closest available JC ion set.
The LM parameters' authors probably revisited the OPC model and created a
separate ion set tuned to that water model.
Hope this helps,
Christina
On Sun, Mar 29, 2020 at 11:27 AM Vlad Cojocaru <
vlad.cojocaru.mpi-muenster.mpg.de> wrote:
> Thanks David,
>
> If course I know I can use whatever set of parameters ... I was just
> wondering whether there is a reason specifically related to the OPC water
> model .... Because the ion parameters are water model specific but the OPC
> water model is loaded with J&C ions for a different water model whereas L&M
> ions are available for OPC ...
>
> Best,
> Vlad
>
> On 29 March 2020 16:36:29 CEST, David A Case <david.case.rutgers.edu>
> wrote:
> >On Sun, Mar 29, 2020, Vlad Cojocaru wrote:
> >>
> >>Second question comes from the fact that while loading the OPC water
> >>model, I noticed that leaprc.water.opc file does not load the Li&Merz
> >>ions for the OPC model (frcmod.ions1lm_126_hfe_opc). Instead, it is
> >>loading the Joung-Chetham monovalent ions for TIP4PEW
> >
> >The default choice for all water molecules (except tip4pd) is to use
> >the
> >Joung-Cheatham parameters for monovalent ions, using Li&Merz parameters
> >for higher charges. As I remember, this was primarily because we had
> >much more experience with the behavior of the JC parameters -- which
> >becomes a bit of a self-fulfilling goal, since most people will use
> >default parameters.
> >
> >My reading of the experience that we do have is that Li&Merz are not
> >much different from JC for monovalents, but others with more direct
> >experience may wish to chime in here.
> >
> >Of course, you are welcome to override the defaults if you wish.
> >
> >....dac
> >
> >
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--
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Christina Bergonzo
Research Chemist
Biomolecular Measurement Division, MML, NIST
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Received on Sun Mar 29 2020 - 14:30:01 PDT
