Solid-state calculations for iterative refinement in quantum crystallography using the multipole model.

Area of Science:

• Quantum Crystallography
• Solid-State Chemistry
• Computational Materials Science

Background:

• Accurate electron density description is crucial for understanding chemical bonding and intermolecular interactions.
• Existing methods like Hirshfeld atom refinement (HAR) have limitations, particularly with gas-phase approximations.
• Transferable form factor approaches offer potential but require careful implementation.

Purpose of the Study:

• To develop and validate a novel quantum crystallographic refinement methodology.
• To utilize theoretical multipole parameters directly from solid-state calculations.
• To improve the accuracy of electron density refinement and hydrogen atom positioning in molecular crystals.

Main Methods:

• Development of the Python3 code ReCrystal for iterative refinement.
• Generation of theoretical multipole parameters using CRYSTAL17 and the XD program.
• Application of the method to molecular crystals of D/L-serine and xylitol.

Main Results:

• The ReCrystal method provides refinement comparable to existing transferable form factor approaches.
• Accurate determination of hydrogen atom positions in xylitol, showing good agreement with neutron diffraction data.
• Demonstrated the effectiveness of periodic boundary conditions in ReCrystal for molecular crystal refinement.

Conclusions:

• The developed methodology offers a robust alternative for charge density studies, particularly focusing on weak interactions.
• ReCrystal allows for multipole parameters derived from high-resolution calculated diffraction data without database dependency.
• This approach effectively separates model and experimental errors, enhancing refinement reliability.