  We completely classify the possible divergence functions for right-angled
Coxeter groups (RACGs). In particular, we show that the divergence of any such
group is either polynomial, exponential or infinite. We prove that a RACG is
strongly thick of order k if and only if its divergence function is a
polynomial of degree k+1. Moreover, we show that the exact divergence function
of a RACG can easily be computed from its defining graph by an invariant we
call the hypergraph index.
