Geometric recipe for superpotentials

Nekrasov, Rosly and Shatashvili observed that the generating function of a certain space
of ${\rm SL}(2)$ opers has a physical interpretation as the effective twisted superpotential
for a four-dimensional $\mathcal{N}=2$ quantum field theory. In this talk we describe the
ingredients needed to generalise this observation to higher rank. Important ingredients are
spectral networks generated by Strebel differentials and the abelianization method. As an
example we find the twisted superpotential for the $E_6$ Minahan-Nemeschansky theory.