The crystal structure is specified by the lattice vectors and the atomic coordinates. The lattice vectors are given as rows of coordinates with respect to a cartesian basis. The unit lenght is an atomic length unit, i.e. the Bohr radius.
In addition to the lattice vectors, the volume has to be given. The lattice vectors will be rescaled such that they span a unit cell with the given volume.
The lattice vectors and optionally the volume must be enclosed within a begin latticevecs and end latticevecs statement.
Example:
begin latticevecs coord 7.22362499411784 -5.04013632834720 0.00000000000000 coord 0.00000000000000 3.95068558900000 2.76187238600000 coord 0.00000000000000 -3.95068558900000 2.76187238600000 volume 157.3848 end latticevecs
The coordinates of the atoms must be enclosed by the statements begin coordinates and end coordinates. Each new element is indicated with a keyword newtype. All coord statements following a newtype statement refer to the new element, until the next newtype keyword is encountered.
The newtype keyword is followed by the atomic type, e.g. O,Si,C, by the spin polarization of the initial charge configuration for this atom, and the size of the muffin-tin sphere (used only for projected DOS, and, if unspecified, is set to 1.0 a.u by default). For instance
newtype Si 0.5 2.4
will define a Si atom. For setting up the initial charge density, a
spin polarization of 
will be used. The muffin-tin sphere around the
silicon atom will have a radius of 2.4 a.u. For non-spin-polarized
calculations, set the spin polarization to 0.
By default, the coordinates following coord are understood to be relative to the basis vectors. To facilitate the input of molecular crystals, it is possible to give them in absolute, cartesian coordinates (a.u.) by specifying the keyword coordinates absolute OUTSIDE the begin/end of the coordinates.
Example:
begin coordinates newtype O 0.17 coord 0.15693515545994 0.10044534718500 -0.10044534718500 coord -0.15693515545994 -0.10044534718500 0.10044534718500 newtype Si 0.0 coord 0.5 0.5 0.5 end coordinates
If there is a center of inversion, the code automatically tries to shift the atomic coordinates such that the crystal has inversion symmetry. If you want to inhibit that, put a line saying:
no restore_inversion
Finally, you can specify whether you want the symmetry-operations to be generated by the code, or if they should be read from the file SYMMETRYOPS. If number_symmetry_ops is followed by -1, then the symmetry operations are determined by the code itself. If number_symmetry_ops is >0, the matrices for the symmetry operation are read in from the file. The file format is the same as the printout in e.g. OUT._0. For an example file, see SYMMETRYOPS
Default: number_symmetry_ops -1