# Configuration interaction

This section discusses three of the closely related configuration interaction (CI) methods available in BAGEL; non-relativistic full configuration interaction (FCI), restricted active space configuration interaction, and relativistic full configuration interaction (RelFCI). These methods have many similarities, but substantial difference in their use. Accordingly, each shall be discussed in a different subsection. Note that keywords which work for one method may not work in another.

- Full configuration interaction (FCI)
- Relativistic full configuration interaction (RelFCI)
- Restricted active space configuration interaction (RASCI)