How do I specify I do not want to perform a specific type of research on my CV?
Usually, in an academic CV, you can distinguish between "Research Activities", which consist of all the research you've done in the past, and "Research Interest", which consist of all the research you want to do in the future. So, someone who would include a topic that you don't list in your research activities without asking you first would be a bit rude. 

However, in order to avoid this kind of cases, and not to be too explicit (that is, not saying "I don't to work on Computational Chemistry"), you can try, in your cover letter or your research interests to put a sentence like "Although I have a good background in Computational Chemistry, my research interests rather lie in ..." or "My background in Computational Chemistry taught me to [...], and I'm now interested in broadening/focusing my interest on [...]". That's a bit more subtle, but I guess the message should pass.