DIRDIF - ORIENT
ORIENT
ORIENT is a program to find the orientation of a molecular fragment
(model) by means of vector search methods (Nordman). The input
model is used for the calculation of interatomic vectors. The
shape function of a single Patterson peak is approximated from
the shape of the origin peak, and it is used for the calculation
of the amount of overlap between neighbouring vectors. Vectors
are selected on weight (including overlap), length, and mutual
separation. A fast cyclic search system, employing increasing
resolution per cycle, leads to the best fitting orientation of
the model in angular space, i.e. the final result of the program
is a set of Eulerian angles (denoted A, B, C) which is applied on
the original model. The selection criterion is the Nordman
'minimum average' function value.
The program is used for structures with known geometry for a
(relatively small) part of the molecule. Note that such molecular
fragment (model) often is available from the users own collection
of structure determinations.
When the user calls for ORIENT, the system will automatically
arrange for the following calculations: first calculate the
Patterson function (programFOUR),
then find the orientation of the
model (program ORIENT), and continue with translation functions
(program TRACOR),
and further structure elucidation (programs
PHASEX and FOUR).