EXPO2014 is able to perform all the steps of the structure solution process by powder diffraction data: indexing, space group determination, estimation of the reflection integrated intensities, structure solution by Direct Methods or/and by direct space/hybrid approaches, model refinement by Rietveld technique.
The program has been designed to:
- require a minimal information as input;
- work automatically;
- reduce the user intervention and facilitate the interaction by means of a user-friendly graphic interface.
X-ray, synchrotron or neutron diffraction data can be used. There are no limits on the number of counts in the pattern.
EXPO2014 is the updated version of EXPO2009. Its main steps are (please, select each topic for more details):
Indexing
An automatic peak search routine generates a list of “d” values corresponding to the experimental diffraction peaks. The values are processed for providing the cell parameters.
Space Group Determination
A statistical analysis of the experimental diffraction intensities compatible with the identified crystal system is performed. This step is able to provide a list of all the possible extinction symbols ranked according to calculated probability values. For each extinction symbol, the corresponding list of compatible space groups (one or more than one) is supplied via graphic interface.
Structure Solution
Structure solution can be carried out by adopting one of the two alternative following approaches:
- Direct Methods for phasing the reflections. The electron density map is calculated and then optimized.
- Direct Space methods for generating trial structure models (compatible with the expected molecular geometry) and selecting that one providing the best agreement with the experimental data.
Rietveld Refinement
The structure model is refined by the Rietveld method.
Each procedure of EXPO2014 can be activated by using a specified command or directive in the input file, or by selecting a specific graphic option. The information about commands, directives and graphic options are contained in this manual.
EXPO2014 creates the following files (in the work directory):
– a direct access file to preserve data and results (name.bin);
– an ascii file containing the Miller indices (hkl) and the experimental structure factor moduli of the generated reflections (name.hkl);
– an ascii file which stores diffraction peak positions if the indexing process has been carried out (name.pea);
– an output file containing information about all the steps of the structure determination process (name.out).
Other files associated to the application of particular strategies can be also generated by EXPO2014.
A. Altomare*, C. Cuocci*, C. Giacovazzo*, A. Moliterni*, R. Rizzi*, N. Corriero* and A. Falcicchio*
*Institute of Crystallography-CNR, via Amendola 122/o 70126 Bari, Italy
angela.altomare@ic.cnr.it
corrado.cuocci@ic.cnr.it
carmelo.giacovazzo@ic.cnr.it
annagrazia.moliterni@ic.cnr.it
rosanna.rizzi@ic.cnr.it
nicola.corriero@ic.cnr.it
aurelia.falcicchio@ic.cnr.it
For questions, problems and suggestions, please, visit http://www.ba.ic.cnr.it/softwareic/expo/contact-us/
We kindly ask you to fill the survey.
The authors are indebted to Giovanni Luca Cascarano and Mariarosaria Mallamo for their help in the development of the graphic environment.
If EXPO2014 is used in the solution process of a structure, whose results are published in a scientific paper, please, include the following reference:
A. Altomare, C. Cuocci, C. Giacovazzo, A. Moliterni, R. Rizzi, N. Corriero and A. Falcicchio, (2013). J. Appl. Cryst. 46, 1231-1235 .