Dear all, 

Im attemoting to create a metal surface and for this am doing tutorial "Polymer interactions with a metal oxide surface". The tutorial says: As the non-bond cutoff distances in the forcefield settings are 9.5 Å, the thickness of your surface must be more than 9.5 Å. For the 0 0 -1 plane it is approximately 13 Å. 

Im my case Im dealing with a Pt surface. So I extended the thinkness up to 15 A (see image 1 attached)

In the same tutorial it says: "Only the top few layers of atoms in the surface will interact with the polymer and the rest of the atoms can be considered to be part of the bulk and therefore have little effect. This means that you can constrain the bulk atoms so that they are not minimized."

Question 1) I was wondering if polymer interacts only the top surface, how come we need to extend the thinkness up to 9.5?

Q 2) In MD settings I see typically 15.5 cutoff is implemented for COMPASS Ewald or vdW. Thats in fact why I put 15 A thinkness rather than 9.5. Could you elaborate a bit on why tutorials recommends 9.5 for cut off distance while the default in most MD settings is 15.5?

Q 3) Could you please take a look at supercell for Pt I created (image 2 attached). I feel like there re too many atoms in there for the study of surface interation. Any comments? Thanks :)

Truly appreciate your comments.

Serene