Structure determination from unindexed powder data from scratch by a global optimization approach using pattern comparison based on cross-correlation functions | JoVE Visualize

Area of Science:

Crystallography
Materials Science
Computational Chemistry

Background:

Crystal structure determination from powder diffraction data is crucial for materials characterization.
Traditional methods often require prior indexing of the powder pattern, limiting their applicability.
Challenges arise with low-crystallinity materials and complex organic/metal-organic compounds.

Purpose of the Study:

To develop a novel ab initio crystal structure determination method from powder diffraction data.
To overcome limitations of existing methods, particularly for unindexed and low-crystallinity samples.
To introduce a user-friendly program, FIDEL-GO, for global structure optimization.

Main Methods:

Developed a global optimization approach using the FIDEL-GO program.
Employed a similarity measure based on cross-correlation functions for comparing simulated and experimental data.
Initiated optimization with random structures across various space groups, fitting unit-cell parameters, molecular position/orientation, and internal degrees of freedom simultaneously.
Implemented a multi-step optimization procedure with clustering and adaptive parameter ranges.
Automated selection of best structures for Rietveld refinement.

Main Results:

Successfully determined crystal structures from unindexed powder diffraction data, even with limited peaks (14-20).
Demonstrated the method's efficacy on nanocrystalline phases of difluoro- and dichloro-quinacridone derivatives.
Solved the structure of a coordination polymer, dichloro-bis(pyridine-N)copper(II).
Showcased applicability to 'problematic' powder patterns and low-crystallinity materials.

Conclusions:

The FIDEL-GO method provides a robust approach for ab initio crystal structure determination from powder data without prior indexing.
The method is particularly valuable for challenging samples, including low-crystallinity materials and complex organic/metal-organic compounds.
FIDEL-GO facilitates structure solution from limited diffraction data and offers potential for high-throughput screening of candidate structures.