charge restrained MD
vincenzo.... at gmail.com
Wed Feb 10 22:02:11 UTC 2016
I know this is a quite old post but i am experiencing similar problems and
I was wondering whether you were able to figure out or not. In my case i
have a zeolite with two metallic centers and i want to track a chemical
reaction which is suppose to be red-ox. In order to force the oxidation
state at least on one of the two metallic centers I tested
both BECKE_RESTRAINT, DDAPC_RESTRAINT. The first one brings very quickly
the whole system to explode moving the lighter atoms first and eventually
all the others in a kind of fully repulsive field. The second approach is
much more stable and allows me to force a charge/spin localization on one
of the two metallic atoms but after a while the mulliken charges have a
discontinuity which get along to the beforementioned atomic "explosion".
Would be extremely halpfull any suggestion
Il giorno mercoledì 29 ottobre 2014 23:03:52 UTC+1, Miłosz Wieczór ha
> Hello cp2k users,
> I'm trying to set up a charge restrained QM/MM MD simulation for a pair of
> QM molecules embedded in TIP3P water. The two molecules can undergo charge
> transfer from a (neutral + radical) to (anion radical + cation) state, and
> ideally I would like to be able to force the spin density to localize on
> one chosen molecule rather than on the other. I imagined that if I restrain
> the charge of the first molecule to -1, it will become an anion radical
> instead of a neutral molecule.
> Anyway, I ran into trouble with technical details. The topic is poorly
> documented so far, so I did some tests with BECKE_RESTRAINT,
> DDAPC_RESTRAINT and MULLIKEN_RESTRAINT, and arrived at following results:
> With BECKE_RESTRAINT, I could obtain the desired spin density distribution
> and produce the .cube file, but the program crashed with a segfault and no
> specific error before the first MD step was done (after the charge
> populations, densities on regular grids and decoupling energy are reported).
> With DDAPC_RESTRAINT, the restraint didn't seem to do anything to the
> system, although MD could proceed with no problem (same parameters as with
> BECKE, only the type of restraint changed).
> With MULLIKEN_RESTRAINT, the Mulliken populations look as desired and the
> MD goes on, but when I visualize the .cube files, I don't see any effect of
> the restraint imposed (the density resides entirely on the second molecule)
> -- which can be an artifact of the specific population analysis method.
> Could anyone explain to me the differences between these approaches, and
> what can cause the crashes with BECKE? Also, should I use
> BECKE/DDAPC_RESTRAINT_A/B in conjunction with BECKE/DDAPC_RESTRAINT, or are
> they mutually exclusive? I will be grateful for any piece of advise.
> In case there are any incompatibilities in the parameters, I attached the
> input file I used for BECKE_RESTRAINT. In other approaches, everything
> except for the restraint secton remained the same.
> Kind regards,
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