The [1][2] element of the standard anisotropic atomic
displacement matrix U, which appears in the structure-factor
term as:
T = exp{-2 pi2 sumi[sumj(Uij hi hj a*i a*j)]}
h = the Miller indices
a* = the reciprocal space cell lengths
These matrix elements may appear with atomic coordinates
in the ATOM_SITE category, or they may appear in the separate
ATOM_SITE_ANISOTROP category, but they may not appear in both
places. Similarly, anisotropic displacements may appear as
either B's or U's, but not as both.
The unique elements of the real symmetric matrix are
entered by row.