Introduction to the special issue on crystal structure prediction

The issue gives a flavour of progress and current research in the area of crystal structure prediction. Developments continue to be made in computational approaches for calculating the stabilities of molecular crystals, as well as for exploring crystal packing possibilities. As exemplified in the sixth blind test of crystal structure prediction, these methods are becoming applicable to complex target structures.

Crystal structure prediction: are we there yet?

This contribution comments on the advances of the latest Crystal Structure Prediction blind test and the challenges still lying ahead.

Report on the sixth blind test of organic crystal structure prediction methods

The results of the sixth blind test of organic crystal structure prediction methods are presented and discussed, highlighting progress for salts, hydrates and bulky flexible molecules, as well as on-going challenges.

Transferable force field for crystal structure predictions, investigation of performance and exploration of different rescoring strategies using DFT-D methods

A general and transferable force field for crystal structure predictions was developed.

An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

An empirically parameterized intermolecular force field is developed for crystal structure modelling and prediction. The model is optimized for use with an atomic multipole description of electrostatic interactions.

Crystal structure prediction of rigid molecules

Methods and results are presented for the crystal structure prediction of rigid molecules using force fields.

Organic crystal polymorphism: a benchmark for dispersion-corrected mean-field electronic structure methods

Route to high-accuracy crystal energy landscapes: From the sixth blind test challenge for crystal structure prediction we compile the POLY59 benchmark set and demonstrate the successful application of modern dispersion-corrected density functional approximations.

How important is thermal expansion for predicting molecular crystal structures and thermochemistry at finite temperatures?

Molecular crystals expand at finite temperatures, which can have appreciable impacts on crystal structure and thermochemical properties. The ability to model thermal expansion using high-level electronic structure methods in the quasi-harmonic approximation and the importance of including thermal expansion effects is assessed for several small molecule crystals.

Generation of crystal structures using known crystal structures as analogues

An investigation into using shape-similarity of molecules to generate putative crystal structures.

Exploring polymorphism of benzene and naphthalene with free energy based enhanced molecular dynamics

The crystal structures of benzene and naphthalene are successfully predicted for atmospheric and high-pressure conditions. Using enhanced molecular dynamics based sampling, we find that mixed structures, which typically cannot be discovered by standard crystal structure prediction methods, are prevalent in the solid forms of these compounds at high pressure.

Using crystal structure prediction to rationalize the hydration propensities of substituted adamantane hydro­chloride salts

The crystal energy landscapes of two model pharmaceutically active chloride salts were used to rationalize the different hydration behaviour of the salts on the basis of the packing of the ions and calculated solvent-accessible volumes in the low-energy structures. The crystal structure of 1-(methylamino)adamantane was characterized and correctly predicted under blind test conditions as the second ranked structure in lattice energy, but the failure to predict the Z′ = 3 structure for the corresponding hydrochloride salt of this relatively simple base illustrates the limits of blind crystal structure prediction.

Effect of packing motifs on the energy ranking and electronic properties of putative crystal structures of tri­cyano-1,4-dithiino[c]-iso­thiazole

A putative crystal structure of tricyano-1,4-dithiino[c]-isothiazole with a layered packing motif is close in energy to the experimentally observed structure and is predicted to possess better electronic and optical properties.

An insight into real and average structure from diffuse X-ray scattering – a case study

Diffuse X-ray scattering from an organic salt has been analysed including modeling of the local structure, explaining relationships between symmetry and extinction patterns, and assessing the sensitivity of the calculated diffuse scattering to the model of the average structure.

Self-assembly modes of glycyrrhetinic acid esters in view of the crystal packing of related triterpene molecules

Molecular organization in unsolvated crystals of ester derivatives of glycyrrhetinic acid reproduces well two preferred modes of self-assembly in solvates of glycyrrhetinic acid and carbenoxolone.

Growth, morphology, structure and character­ization of L-histidinium di­hydrogen arsenate orthoarsenic acid single crystal

Hirshfeld surface analysis, piezoelectricity and ferroelectricity are reported for the first time in L-histidinium dihydrogen arsenate orthoarsenic acid (LHAS) single crystals.

Bond-length distributions for ions bonded to oxygen: alkali and alkaline-earth metals

Bond-length distributions have been examined for 55 configurations of alkali-metal ions and 29 configurations of alkaline-earth-metal ions, for 4859 coordination polyhedra and 38 594 bond distances (alkali metals), and for 3038 coordination polyhedra and 24 487 bond distances (alkaline-earth metals).

On the effective ionic radii for ammonium

A set of effective ionic radii corresponding to different coordination numbers (CNs) and compatible with the radii system by Shannon [Acta Cryst. (1976), A32, 751–767] has been derived for ammonium: 1.40 Å (CN = IV), 1.48 Å (CN = VI), 1.54 Å (CN = VIII) and 1.67 Å (CN = XII).

Structure and topology of three-dimensional hydrocarbon polymers

A new family of three-dimensional hydrocarbon polymers with no known structural analogs which are more energetically favorable than benzene is proposed.

Modulated crystal structure of InMo₄O₆

Tetragonal InMo₄O₆ is a metal-rich compound with infinite chains of edge-sharing Mo₆ clusters; the (3 + 1)-dimensional modulated structure hosts In₆ and In₇ oligomers in channels along [001] – this leads to two different kinds of disorder.

Structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts; role of ammonium ions in crystal structure formation

Structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts, and the roles of ammonium ions in the crystal structure formation are reported.