Vibration modes and phonons

Have you set up the local environment?

If not, do that now before proceeding.

In this set of exercises we will use the method of finite-differences implemented in Siesta to compute force constants in real space. We will explore the cases of a crystal and a molecule. In the former case we will focus on the need of a supercell to represent the real-space force constants, while in the second we will understand how to visualize the vibrational modes.

Note

Phonon calculations can be very sensitive to numerical artifacts such as those derived from the eggbox effect. Be sure to have the rest of your simulation parameters already converged as best as you can before running the actual force constant matrix calculations.

• Phonon dispersion of bulk Si
• Modes of vibration of the benzene molecule