## Atom.type — CHARMM atom type

> This is a CHARMM AtomType object (see Section 6.24), which tracks per-type rather than per-atom properties such as the element symbol, radius and atomic mass. If the model has not yet had CHARMM atom types assigned, it is `None`.

> The atom type can also be changed by assigning a CHARMM atom name (as a string, such as 'CT1'), or `None`, to it. This can be useful when using BLK residues, which otherwise use the same atom type (`‘undf’`) for every atom.

> (Only available for models, not template structures.)