First, try to define your system with atoms. For example, you mentioned some media. Can you define that media in terms of atoms? If you can define your system with atoms, then you shall be able to do some atomic level calculations on it.
HOMO LUMO levels are not quite useful for your purpose. It seems that you are currently studying chemisorption, what you should focus on should be reactivity and regioselectivity, I suggest you pay attention to papers related to conceptual density functional, which has been heavily employed for study this kind of problem. For example, in the framework of CDFT, softness is closely related to reactivity, while Fukui function and dual descriptor are often used to predict favourable reactive sites. See Chem. Rev. 2003, 103, 1793-1873, Chem. Rev. 2011, 111, PR43 and Acta Phys. -Chim. Sin., 2009, 25(3), 590 for review. My code Multiwfn (http://sobereva.com/multiwfn) can very easily calculate almost all quantities defined in the CDFT framework based on .wfn file outputted by Gaussian, see 3.100.16 for introduction and Section 4.100.16 for example.