Isaak Daniels isaakdan... at gmail.com
Tue Aug 23 12:23:17 UTC 2011

Can I also have it so that in the non-vapor box, gas molecules can
enter that box and one can also import coordinates of a crystal, with
this box having QM?

Thank you

On Aug 23, 3:21 am, Matt McGrath <obfis... at gmail.com> wrote:
> Hmm.  I was thinking about that, and I didn't think it would work
> before I responded to your original question.  But now, I'm not so
> sure.  If you set all the MM interactions in the vapor box to have
> epsilon=0 and no charges (so you don't need Ewald sums), then you have
> an ideal gas, so...maybe.
> A quick way to check would be to try it with MM in both boxes, but set
> all the LJ parameters and charges equal to zero in the vapor box.
> Choose it to be large enough that the density doesn't really change
> over the course of the simulation, don't do any molecule displacements
> in the vapor box, and compare it against GCMC with a different code.
> One concern I have is that, on swap moves, the code is going to check
> for overlaps in the vapor box, which it should do for true GCMC.  If
> you try this test and get an answer that is close, and you feel
> comfortable changing the source code, I can let you know which lines
> to change to remove those checks so we can see if it works.  I know of
> codes that do GCMC as basically GEMC with a box that has no
> interactions in it (and is big...500 molecules or more), so this
> doesn't seem so different.
>                                               Cheers, Matt
> On Aug 22, 10:57 pm, Isaak Daniels <isaakdan... at gmail.com>
> wrote:
> > Can one do it so that the box not of interest (representing the
> > environment) is MM while the other is done with QM, so one can avoid
> > the pitfalls of enlarging the box?
> > Thank you
> > On Aug 21, 7:42 pm, Matt McGrath <obfis... at gmail.com> wrote:
> > > Hi Isaak.  Unfortunately, this isn't really possible at the moment,
> > > unless you do Gibbs ensemble Monte Carlo and make the second box huge,
> > > i.e. essentially a reservoir.  Of course, if you're using any grid-
> > > based method to compute the energy (Quickstep, Ewald) this adds a
> > > whole lot of expense to the simulation as well, and probably isn't
> > > worth it.
> > > GCMC has been in the pipeline for a while (there have been issues with
> > > the choice of reference state for QS calculations with GCMC), and is
> > > the next big project on my list.  I'm about 30% done with the current
> > > project (making the MC routines more streamlined), so it might get
> > > implemented in the next year...but that's just a guess.  Could be six
> > > months, could be a couple years, so if you're working on a major
> > > project, it's probably best to use a different code.  Sorry!
> > >                                 Cheers, Matt
> > > On Aug 21, 2:51 am, Isaak Daniels <isaakdan... at gmail.com> wrote:
> > > > Is there a way to run a sort of GCMC on Cp2k?
> > > > Thank you

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