eigs for a discrete system

I have to calculate the eigevalues  of a very large discrete systems. Therefore I chose to use eigs function. Morevoer, I haven’t the analytical expression of the jacobian so I use eigs(Afun….). Now, my goal is to evaluate just some of the overall eigenvalues spectrum, precisely the set close to the unit circle in the imaginary plane but eigs only support options like ‘SM’,’SR’….Colud anyone help me to solve this problem? 
Thank you in advance