type
Controls the representation of the cell lattice, which can be: 
1) 
conventional (the lattice is constructed using 
n1, 
n2, 
n3 conventional cells; 2) 
primitive (the lattice 
is constructed using 
n1, 
n2, 
n3 primitive cells); 
3) 
wigner (the lattice is constructed using 
n1, 
n2, 
n3 Wigner-Seitz cells); 4) 
parallelepiped (the lattice is filtered 
by a generic parallelepiped volume, with length parameters 
v1, 
v2, 
v3 and angle parameters 
v12, 
v13, 
v23); 
5) 
sphere (the lattice is filtered by a sphere with radius 
v1); 
6) 
projection (the lattice is represented by its stereographic projection).
  
Example: <cell ... type="conventional"/> (default)
Allowed values: conventional, primitive
wigner, rhombus, sphere, 
projection (optional)
n1, n2, n3
Control the number of lattice cells created along 
the directions defined by the vectors 
a, 
b, 
c, 
when 
type is 
conventional, 
primitive
or 
wigner. Indicating some or all of these parameters when 
the cell type does not require them is flagged as an error.
Example: <cell ... n1="1" n2="2" n3="3"/> (default)
Allowed values: positive integer (optional, coupled)
v1, v2, v3, v12, v13, v23
When 
type is 
parallelepiped, these six parameters are needed 
to indicate the edge lengths and angles of the filtering parallelepiped.
Each angle must be smaller than the sum of the other two and must be larger 
than the absolute difference of the other two, otherwise an error is produced.
When 
type is 
sphere, the 
v1 parameter is needed to
indicate the radius of the filtering sphere. Setting parameters that are 
not required for a given cell type is flagged as an error.
Example: <cell ... v1="5.0" v2="6.0" v3="7.0"
v12="60.0" v13="70.0" v23="80.0"/> (no default)
Allowed values: positive real (required)