# Molecule specification

Molecule, starting with `"title" : "molecule"`, is one of the basic input blocks specifying important information such as basis sets and geometry for the input system. The user has to specify the contents of this block in order to run the calculation.

- Required keywords
- Optional keywords
- Basis sets
  - Orbital basis sets
  - Density fitting basis sets
    - Examples
  - Auxiliary basis sets
    - Example
  - Effective core potential (ECP) basis sets
    - Example
  - User defined basis sets
    - Example
- Other features
  - Dummy atoms
    - Example
- Updates to Molecule Specification
  - Useful Parameters to Change
- References