[lammps-users] Fixing of bottom layers during indentation

Dear Sir/Madam,
I am working on multilayer metal coatings. I have an aluminium substrate over which I need to coat Al/Ni bilayers. Experimentally film only hardness is determined and hence substrate effect is neglected. To obtain the film only hardness in MD, fixing the bottom layer of the coating will give the same result or should I seperately specify the substrate.
What should be the thickness of substrate when compared to coating thickness for getting a correct result. Is there any thumb rules?

Since this is much more about how to do the science than actually issues specific to LAMMPS, my suggestion is that you search the published literature for studies similar to what you want to conduct and take from there the justification of your choices and simulation settings and details.