Examples of GCMC of gas adsorption onto a surface

GULP
1

Dear users

Are there any example gin files for GCMC of gas adsorption?

Specifically I am interested in simulating calorimetry data, and calculating the isosteric heat of adsorption.

I’m struggling to work out where to start, after looking at the examples that are bundled with GULP, and in particular how to define a volume close to the surface i.e. where the adsorption would happen - or am I thinking about this wrong?

Any responses kindly received,

Ian Shuttleworth

2

Hi Ian,

At the moment the option to simulate adsorption is really only implemented for 3D systems, since the volume must be specified. It sounds from your message that you are wanting to adsorb at a 2D interface? If so, the problem becomes how to limit the region above the surface to define the trial volume for insertion (which obviously must be finite). In principle, an option could be added to specify an upper distance from the surface for creation of species, but I’m afraid this isn’t present at the moment. Of course use of a 3D supercell is one way round this.

Best regards,

Julian

3

Dear Julian

Thank you very much for your reply.

I think I phrased my question badly, it’s adsorption on a surface rather than between an interface that I want to be looking at. I’m using a 3D cubic supercell then setting a larger z dimension compared to the x-y dimensions which are parallel to the plane of the surface.

It was really just efficiency I was thinking about - a lot of attempts would be made to create atoms in the slab, and I want the slab to be thick because I want a good phonon profile for these simulations.

Is there any sense in trying to replace one of the surfaces with a ‘mirror’ rather than a surface, or just stopping the simulation periodically and removing all molecules above a certain height above the surface? Again, I’m just thinking about rate of convergence.

Is it possible to get more output during gcmc? My simulations complete and the final structure writes to the standard output, but adding an ‘output’ statement doesn’t write the final structure to e.g. an xyz file.

Also, is there any way to get movie output, in the same way you can in md? If I’m overlooking something obvious with this I apologise

With thanks

Ian