Alanine dipeptide is one of the simplest molecules that exhibits some important features common to larger biomolecules.

Alanine dipeptide has more than one long-lived conformation, which are characterized by the dihedral angles of the backbone. We color carbons in blue, hydrogens in white, oxygen in red and nitrogen in blue, i.e. the torsional angle $\phi$ is C-N-C-C, while $\psi$ is N-C-C-N along the backbone.

In this exercise, we are going to map out the potential energy surface of alanine dipeptide as a function of the dihedral angles $\phi$ and $\psi$.

With this knowledge at hand, we will fix the dihedral angles and perform geometry optimization for all remaining degrees of freedom.