The seventh blind test of crystal structure prediction: structure generation methods

The results of the seventh blind test of crystal structure prediction are presented, focusing on structure generation methods.

The seventh blind test of crystal structure prediction: structure ranking methods

The results of the seventh blind test of crystal structure prediction are presented, focusing on structure ranking methods.

Polymorph sampling with coupling to extended variables: enhanced sampling of polymorph energy landscapes and free energy perturbation of polymorph ensembles

A design is tested for a polymorph search algorithm relevant for enhanced sampling of crystal structures based on the relation between internal molecular structure variables and corresponding crystal polymorphs as representative of the inherent vapor to crystal transitions that exist in nature. Molecules are represented as extended variables within a thermal reservoir. Unit-cell variables are generated using pseudo-random sampling incorporating a harmonic coupling to extended variables.

Assessment of the exchange-hole dipole moment dispersion correction for the energy ranking stage of the seventh crystal structure prediction blind test

Density-functional calculations using numerical atomic orbitals and the exchange-hole dipole moment dispersion model were applied to the energy ranking stage of the seventh crystal structure prediction blind test. This methodology gave successful predictions of the experimentally isolated polymorphs as being low in energy for three of the compounds considered, and for one additional compound upon inclusion of a vibrational free-energy correction.

Contrasting conformational behaviors of molecules XXXI and XXXII in the seventh blind test of crystal structure prediction

The conformational energies and crystal energy landscapes for molecules XXXI and XXXII from the seventh blind test of crystal structure prediction are investigated with a variety of electronic structure methods. Whereas molecule XXXI can be modeled relatively straightforwardly, molecule XXXII proves challenging even for state-of-the-art quantum chemistry techniques.

Spin reorientation and the interplay of magnetic sublattices in Er₂CuMnMn₄O₁₂

We show that the interplay of multiple magnetic sublattices in Er₂CuMnMn₄O₁₂ leads to four magnetic phase transitions characterized by the onset of ferrimagnetic order, spin-reorientation, spin canting, and the polarization of Er ions. While we elucidate numerous features of this complex magnetic system, the exact nature of the low-temperature coupling between erbium and manganese, and the origin of a k = (0, 0, ½) modulation, remain intriguing topics for future studies.

Crystal structure of the incommensurate modulated high-pressure phase of the potassium guaninate monohydrate

Incommensurate phase of potassium guaninate monohydrate is the first example of a modulation in purine derivatives and of a high-pressure incommensurate crystal structure to be solved for an organic compound.

From `crystallographic accuracy' to `thermodynamic accuracy': a redetermination of the crystal structure of calcium atorvastatin trihydrate (Lipitor^®)

The crystal structure of calcium atorvastatin trihydrate was redetermined from previously published synchrotron powder diffraction data to give a much-improved agreement with two independent density-functional theory calculations.

Synthesis and structural study of the partially disordered complex hexagonal phase δ₁-MnZn_9.7

A detailed structural characterization of the δ₁-MnZn_9.7 phase is presented.

Crystal structure and compressibility of magnesium chloride heptahydrate found under high pressure

In-situ diffraction measurements reveal that magnesium chloride forms a unique high-pressure phase, a heptahydrate, above 2 GPa. The hydrogen-bonding structure appears to contain orientational disorder.

Crystal structure of nickel orthovanadate (Ni₃V₂O₈) at 299 (3) K and 1323 (8) K: an X-ray diffraction study

The structure of Ni₃V₂O₈ was studied using X-ray diffraction at temperatures of 299 and 1323 K. No phase transition at high temperature is observed. The variation in V—O bond length is small as compared with the Ni—O bond due to its high rigidity.

The incommensurate composite Y_xOs₄B₄ (x = 1.161)

Tetragonal Y_xOs₄B₄ (x = 1.161) is an incommensurate composite of columns of Y atoms in a three-dimensional Os₄B₄ framework. The structure was refined using the superspace approach.

Morphological control for hollow rod crystals of a photochromic di­aryl­ethene on spherulites by surface properties of substrates

1,2-Bis(3,5-di­methyl-2-thienyl)perfluoro­cyclo­pentene formed its own spherulites by sublimation onto the hydro­philic surfaces of the (0001) planes of α-quartz and sapphire substrates. The formation of different morphologies of these spherulites was attributed to the surface properties of each substrate. Depending on the morphology of the spherulites, hollow rod crystals with cross sections of different sizes and shapes and branching structures were generated on the surfaces of the spherulites.

Atypical phase transition, twinning and ferroelastic domain structure in bis­(ethylenedi­ammonium) tetra­bromozincate(II) bromide, [NH₃(CH₂)₂NH₃]₂[ZnBr₄]Br₂

A unique phase transition, twinning and ferroelastic domain structure in [NH₃(CH₂)₂NH₃]₂[ZnBr₄]Br₂ is found. The new additional domain structure is observed at the phase transition on heating, which is preserved after cooling to room temperature.