The [1] element of the three-element vector used to transform
               fractional coordinates in the ATOM_SITE category to Cartesian
               coordinates in the same category. The axial alignments of this
               transformation are described in _atom_sites.Cartn_transform_axes.
               The rotation matrix is defined in
               _atom_sites.Cartn_transf_matrix[][].
               |x'|              |11 12 13| |x|               |1|
               |y'|Cartesian = |21 22 23| |y|fractional + |2|
               |z'|              |31 32 33| |z|               |3|