Rietveld refinement and structure verification using `Morse' restraints

Abstract

A new restraint scheme for Rietveld refinement based on Morse bond energy potential is introduced, in which the asymmetry of the Morse potential allows the refinement to `break' the incorrectly placed bonds. The analysis of bond‐length distributions at different values of restraint strength reveals a visible difference in behavior of wrong and correct structures, which can be detected using robust statistical methods. This fact is employed as a basis for a novel structure verification criterion. The approach is demonstrated on known difficult cases of acetolone and γ‐quinacridone and used for the Rietveld refinement of N‐(6‐phenylhexanoyl)glycyl‐L‐tryptophanamide, an organic molecule of a potential anxiolytic containing 32 non‐H atoms and 14 single bonds. The results are verified using density functional theory calculations with periodic boundary conditions.

Syntheses of Nitronium Salts: A New Strategy towards Solid Nitronium Monosulfates

“…coordinate difference of 0.174 Å as defined in the van der Streek criterion for crystal structure correctness well below the proposed threshold of 0.35 Å. The structure was also successfully validated by the refinement with breakable restraints . The refinement details and crystallographic data can be found in Supporting information .…”

Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional theory (DFT-D)

“…FEFNOV (0.41 Å ) (Bushmarinov et al, 2012). The unit cell contracts by 3% in the a direction, indicating a minor temperature effect.…”

Highly Luminescent, Water‐Soluble Lanthanide Fluorobenzoates: Syntheses, Structures and Photophysics, Part I: Lanthanide Pentafluorobenzoates

“…The resulting structure was refined and verified by using as ymmetrized modification of Morse restraints and statistical analysis of bond-length distributions at different values of penalty weighting. [44] Still, given the relatively low quality of the powder pattern and the relative complexity of the studied structure (44 non-hydrogen atoms), we used periodic DFT calculations to check the refinement results and obtain more reliable complex geometry. [45] The calculation was performed by using the PW-PBE approach with Grimme correction [46] as implemented in VASP, [47] with af ixed unit cell and 680 eV energy cutoff.…”