A model’s unit cell is, at any given time, one of the following:

Value Description
none The model has no unit cell (i.e. it is non-periodic)
cubic The model's unit cell is cubic, with A=B=C and alpha=beta=gamma=90
orthorhombic The model's unit cell is an orthorhombus, with any cell lengths and alpha=beta=gamma=90
parallelepiped The model's unit cell is monoclinic or triclinic, with any cell lengths and angles