THE SIR99 PACKAGE: THE VERY
LAST PROGRESSES
M.C.Burla3,
M.Camalli2, B.Carrozzini1,
G.Cascarano1,
C.Giacovazzo1, A.G.G.Moliterni1,
G.Polidori3, R.Spagna2
1 Istituto di Ricerca per
lo Sviluppo di Metodologie Cristallografiche, CNR, Bari, Italy.
2 Istituto di
Strutturistica Chimica 'G.Giacomello', CNR, Roma, Italy.
3 Dipartimento di
Scienze della Terra, Universita', Perugia, Italy.
E-mail: g.cascarano@area.ba.cnr.it
Keywords:
computer program, direct methods
SIR97[1], the heir of Sir92[2], has been
recently distributed. It is able to solve up to medium size
crystal structures and to completely refine the model structure,
providing at the end publication tables and CIF files.
A powerful graphic interface can be used to
study the resulting model and is able to guide the user for an
efficient and fast structure refinement.
The Sir99 package, not yet distributable, will
present new performances:
- Restraints
- Restraints are incorporated in the least
squares refinement as if they were additional experimetal
observations. Restraints on distances, angles and on
expected planar groups have been introduced. Furthermore,
floating origin restraints are generated automatically by
the program, when required by the space group symmetry.
- Disorder
- Sir99 handles structures which contain
mixture of different atoms occupying the same site. So
far the program uses up to five atomic species and
relative occupances for this kind of mixed atom site. A
linear restraint of site occupation factors restraints
the sum to be constant.
- Solution of larger structures
- Sir97 was unable to solve medium size
structures ( > 200 atoms in asymmetric unit ) owing to
inefficiency of the strategy and to memory usage
problems. We have improved the procedure. Some examples
of large structures ( App, Rubredoxin, …) are solved by
the present version of Sir99.
- Altomare,
A., Burla, M.C., Camalli,
M., Cascarano, G., Giacovazzo, C., Guagliardi, A.,
Moliterni, A.G.G., Polidori, G., Spagna, R. (1998) J.
Appl. Cryst., submitted
- Altomare, A., Cascarano, G., Giacovazzo,
C., Guagliardi, A., Burla, M.C., Polidori, G. &
Camalli, M. (1994). J. Appl. Cryst. 27, 435