Using the optimized geometry,
the Hessian can be calculated, and its eigenvalues and eigenvectors found.
These turn out to be very important -
they relate to the vibrational motion of the molecule.
They allow us to calculate the normal modes of vibration, and to visualize them:
Calculated
frequency: 2169cm-1 (experimental value: 1595 cm-1)
Calculated
frequency: 4141cm-1 (experimental value: 4070 cm-1)
Calculated
frequency 4392 cm-1 (experimental value 4188cm-1)