              The [1][1] element of the anisotropic atomic displacement\
               matrix B, which appears in the structure factor term as:\
\
               T = exp{-1/4 sum~i~[sum~j~(B~ij~ h~i~ h~j~ 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.\
\
               The IUCr Commission on Nomenclature recommends against the use\
               of B for reporting atomic displacement parameters. U, being\
               directly proportional to B, is preferred.