
I am studying statistical mechanics and force-fields, and I see a lot of this formula being thrown around with no explanation:
$$U_{\mathrm{dihedral}} = \begin{cases}
k(1+\cos (n\psi + \phi)),& n>0 \\
k(\psi - \phi)^2, & n=0 \\
\end{cases} $$
The only explanation I read is: this...