Where does Computer Science background students fit in Theoretical Physics I am basically an Electronics student - background in Computer Science (that's where I want to work). I applied for an internship in USA in a research institute where the group is focused in Theoretical Condensed Matter Physics, Chemical Physics, Physical Chemistry, Materials Science.

I got selected. Now, I would like to know where area could someone with CS background  would actually work on?

I am looking for a detailed answer.
Given a background in CS, that probably means you have a sophisticated view of software development—at least one that is far more advanced than the average physicist or materials scientist. 

It seems to me that you would probably find that you would be working as a programmer on a computational project: perhaps a new numerical method needs to be implemented, or the performance or functionality of the existing code base needs to be improved. Or perhaps they want somebody to help prototype new interfaces between experimental hardware and computer hardware or software? There are a lot of possibilities.