Periodic CC methods in FHI-aims

This is a tutorial on how to perform calculations involving correlated wave function methods (MP2, CC, etc.) with FHI-aims particularly for solids but for molecular systems as well. The calculations will be performed using the "Coupled Cluster for Solids" (CC4S) code developed in the Group of Andreas Grüneis at the TU Wien in combination with the recently published interface for FHI-aims, CC-aims.

In terms of correlated wave function methods that are available in CC4S, we will limit ourselves to Moller-Plesset perturbation theory of second order (MP2) to keep the computational cost of the tutorial calculation at a minimum. If you wish to perform more advanced calculations involving coupled-cluster (CC) theory, you can follow the exact same steps presented in this tutorial. The only thing you need to adapt is the input file for CC4S, which specifies which algorithm shall be run.

The tutorial consists of two parts: In the first part, the MP2 correlation energy of the paracetamol molecule will be determined and the importance of the basis set and reaching the complete basis set limit will be demonstrated. The second part (in progress) will extend the discussion to periodic systems, by calculating the MP2 correlation energy of the LiH bulk solid. In this context, the finite-size error as the primary source of error for periodic MP2/CC calculations will be discussed.