Benchmarking crystal structure refinement: A systematic study on Hirshfeld atom refinement.

Area of Science:

• Crystallography
• Computational Chemistry
• Quantum Chemistry

Background:

• Hirshfeld atom refinement (HAR) is crucial for accurate crystal structure analysis.
• Conflicting recommendations exist regarding optimal wavefunction calculation parameters for HAR.
• Amino acid structures provide reliable benchmarks due to high experimental data quality.

Purpose of the Study:

• To systematically investigate the impact of wavefunction calculation parameters on HAR.
• To resolve discrepancies in the literature regarding recommended HAR procedures.
• To provide guidance on selecting appropriate computational methods for HAR.

Main Methods:

• Employed a comprehensive permutation of refinement parameters (2496 refinements per amino acid).
• Utilized high-quality amino acid crystal structures as test cases.
• Compared gas-phase calculations with solvent models and various quantum chemical methods.

Main Results:

• Solvent models consistently improved HAR results compared to gas-phase calculations.
• The pure Hartree-Fock method outperformed all tested density functional theory (DFT) methods.
• Performance differences were observed across various tested parameters and structures.

Conclusions:

• Careful selection of the level of theory is critical for successful HAR.
• The pure Hartree-Fock method is recommended over tested DFT methods for polar organic molecules in HAR.
• This study offers a clear overview of method and parameter performance in HAR.