Abstract

The EXPO package [1] is a computing program able to successfullyprovide the structure solution by starting from minimal information:the experimental powder diffraction pattern and the chemical formulaof the compound to investigate. EXPO can be used for solving organic,inorganic, metalorganic structures for a large variety of applications.Automation and efficiency are suitably combined in EXPO forperforming all the steps of the solution process: indexation, spacegroup determination, intensity extraction, structure solution, modeloptimization, Rietveld refinement.Automation. Default strategies, identified as the most effective,are selected for carrying out the solution process automatically andquickly. They may fail when the experimental data resolution is badand/or the structure complexity is remarkable. In these cases, EXPOcan promptly switch to appropriate strategies by profiting by a userfriendly graphical interface.Efficiency. Innovative theories and computing procedures aimingat making straightforward all the steps of the solution process areintegrated in EXPO and widely tested. EXPO is continuously updatedand optimized in terms of both computing efficiency and graphicalperformances.In EXPO the two stages based ab initio approach (in the first stagethe intensities are extracted; in the second, the reflections are phasedby Direct Methods) [2] is the automatic choice. The model providedby Direct Methods is usually partial and approximate because of wellknown unavoidable problems in powder diffraction (overlapping,background, preferred orientation). It can be optimized by default [3],[4] and/or non-default strategies [5], [6] which are able to reduce theerrors depending on the limited experimental resolution.A very recent study has regarded a new and more effective figureof merit [7], alternative to the classical one. It is able to pick up thephasing trial corresponding to the best solution among several feasibleones.Non ab initio method, requesting the knowledge of the expectedmolecular geometry and based on Simulated Annealing technique[8, 9], can optionally be attempted particularly in case of solution oforganic compounds.Examples of successful automatic runs by EXPO will be discussedin addition to available special strategies.

Autore Pugliese

• Altomare Angela , Moliterni Anna , Cuocci Corrado , Rizzi Rosanna

Tutti gli autori

• A. Altomare; C. Cuocci; C. Giacovazzo; A. Moliterni; R. Rizzi

Titolo volume/Rivista

Acta crystallographica. Section A, Crystal physics, diffraction, theoretical and general crystallography

Anno di pubblicazione

2011

ISSN

1600-8596

ISBN

Non Disponibile

Numero di citazioni Wos

Nessuna citazione

Ultimo Aggiornamento Citazioni

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Numero di citazioni Scopus

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Ultimo Aggiornamento Citazioni

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Settori ERC

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Codici ASJC

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