Computational Chemistry: calculation of sterical effects
I think that you're searching for non-covalent interactions; if so, here's the usual Wikipedia link, https://en.wikipedia.org/wiki/Non-covalent_interactions

But more importantly here's the paper describing the software, http://pubs.acs.org/doi/abs/10.1021/ja100936w and here's Prof Rzepa's blog with 'non-covalent interaction' searched, http://www.ch.imperial.ac.uk/rzepa/blog/?s=non-covalent+interaction

That's the start, post again when you want to know how to implement it.