Table 2. Constraints for crystal systems and command line options for the C++ implementation of CELLOPT (Massa, 1999 ▸).

‘c.l. option’ denotes the command line option to set the respective crystal system. ‘#var.’ denotes the number of independent variables for the optimization algorithm [cf. equation (1)].

Crystal system	Constraints	c.l. option	#var.
Triclinic	None	-xa	6
Monoclinic	α = γ = 90°	-xm	3
Orthorhombic	α = β = γ = 90°	-xo	3
Hexagonal	a = b, α = β = 90°, γ = 120°	-xh	2
Tetragonal	a = b, α = β = γ = 90°	-xt	2
Cubic	a = b = c, α = β = γ = 90°	-xc	1