Disorder to order: how halide mixing in MAPbIBr perovskites restricts MA dynamics.

Mixed-halide lead perovskites are of particular interest for the design of tandem solar cells currently reaching record efficiencies. While halide phase segregation upon illumination of mixed perovskites is extensively studied, the effect of halide disorder on A cation dynamics is not well understood, despite its importance for charge carrier diffusion and lifetime. Here, we study the methylammonium (MA) reorientational dynamics in mixed halide MAPbIBr perovskites by a combined approach of experimental solid-state NMR spectroscopy and molecular dynamics (MD) simulations based on machine-learning force-fields (MLFF).

Comparing GIPAW with numerically exact chemical shieldings: The role of two-center contributions to the induced current.

In this study, we benchmark density functional theory gauge-including projector-augmented-wave (GIPAW) chemical shieldings against molecular shieldings for which basis set completeness has been achieved [Jensen et al., Phys. Chem.

Microscopic (Dis)order and Dynamics of Cations in Mixed FA/MA Lead Halide Perovskites.

Recent developments in the field of high efficiency perovskite solar cells are based on stabilization of the perovskite crystal structure of FAPbI while preserving its excellent optoelectronic properties. Compositional engineering of, for example, MA or Br mixed into FAPbI results in the desired effects, but detailed knowledge of local structural features, such as local (dis)order or cation interactions of formamidinium (FA) and methylammonium (MA), is still limited. This knowledge is, however, crucial for their further development.

The Rich Solid-State Phase Behavior of dl-Aminoheptanoic Acid: Five Polymorphic Forms and Their Phase Transitions.

The rich landscape of enantiotropically related polymorphic forms and their solid-state phase transitions of dl-2-aminoheptanoic acid (dl-AHE) has been explored using a range of complementary characterization techniques, and is largely exemplary of the polymorphic behavior of linear aliphatic amino acids. As many as five new polymorphic forms were found, connected by four fully reversible solid-state phase transitions. Two low temperature forms were refined in a high ' crystal structure, which is a new phenomenon for linear aliphatic amino acids.

The Role of Connectivity on Electronic Properties of Lead Iodide Perovskite-Derived Compounds.

We use a layered solution crystal growth method to synthesize high-quality single crystals of two different benzylammonium lead iodide perovskite-like organic/inorganic hybrids. The well-known (CHCHNH)PbI phase is obtained in the form of bright orange platelets, with a structure comprised of single ⟨100⟩-terminated sheets of corner-sharing PbI octahedra separated by bilayers of the organic cations. The presence of water during synthesis leads to formation of a novel minority phase that crystallizes in the form of nearly transparent, light yellow bar-shaped crystals.

Symmetry, Dynamics, and Defects in Methylammonium Lead Halide Perovskites.

In order to better understand the structure and dynamics of methylammonium lead halide perovskites, we performed NMR, NQR, and DFT studies of CHNHPbI in the tetragonal and cubic phase. Our results indicate that the space group of the tetragonal phase is the nonpolar I4/mcm. The highly dynamic methylammonium moiety shows no indication of the occurrence of additional orientations of the C-N bond close to the c-axis at temperatures approaching the cubic phase.

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

The sixth blind test of organic crystal structure prediction (CSP) methods has been held, with five target systems: a small nearly rigid molecule, a polymorphic former drug candidate, a chloride salt hydrate, a co-crystal and a bulky flexible molecule. This blind test has seen substantial growth in the number of participants, with the broad range of prediction methods giving a unique insight into the state of the art in the field. Significant progress has been seen in treating flexible molecules, usage of hierarchical approaches to ranking structures, the application of density-functional approximations, and the establishment of new workflows and `best practices' for performing CSP calculations.

Anionogenic mixed valency in KxBa1-xO2-δ.

We have synthesized members of an isostructural solid solution series KxBa1-xO2-δ (x < 0.41, δ < 0.11) containing mixed-valent dioxygen anions.

Finite-field implementation of NMR chemical shieldings for molecules: direct and converse gauge-including projector-augmented-wave methods.

Two finite-field implementations for the calculation of chemical shieldings of molecular systems using a plane-wave basis set and the Gauge-Including Projector-Augmented-Wave method are presented. The direct approach mimics the nuclear magnetic resonance experiment in that it puts the molecule in a uniform magnetic field and obtains shieldings from the current response. The other is based on the recently introduced "converse method" [T.

Hydrogen bonding and chemical shift assignments in carbazole functionalized isocyanides from solid-state NMR and first-principles calculations.

Carbazole functionalized polyisocyanides are known to exhibit excellent electronic properties (E. Schwartz, et al., Chemistry of Materials, 2010, 22, 2597).

First-principles modelling of magnesium titanium hydrides.

Mixing Mg with Ti leads to a hydride Mg(x)Ti((1 - x))H(2) with markedly improved (de)hydrogenation properties for x ≤ 0.8, as compared to MgH(2). Optically thin films of Mg(x)Ti((1 - x))H(2) have a black appearance, which is remarkable for a hydride material.

A solid-state NMR and DFT study of compositional modulations in Al(x)Ga(1-x)As.

We have conducted (75)As and (69)Ga Nuclear Magnetic Resonance (NMR) experiments to investigate order/disorder in Al(x)Ga(1-x)As lift-off films with x∼ 0.297 and 0.489.

Theoretical study of the stable radicals galvinoxyl, azagalvinoxyl and wurster's blue perchlorate in the solid state.

Calculations on crystalline organic radicals were performed to establish the ground states of these materials. These calculations show that the radicals may interact, depending on their orientation in the crystal structure. For galvinxoyl, a second structure is proposed which is similar to that of azagalvinoxyl, in which the radicals form pairs.

Thermodynamic stability of boron: the role of defects and zero point motion.

Its low weight, high melting point, and large degree of hardness make elemental boron a technologically interesting material. The large number of allotropes, mostly containing over a hundred atoms in the unit cell, and their difficult characterization challenge both experimentalists and theoreticians. Even the ground state of this element is still under discussion.

Anionogenic ferromagnets.

Magnetism in molecules and solids is understood to originate from atoms in that part of the periodic table where a particular value of the angular momentum appears first (i.e., the 2p, 3d, and 4f series).

Modeling the polymorphism of pentacene.

Thin films of pentacene are known to crystallize in at least four different polymorphs. All polymorphs are layered structures that are characterized by their interlayer spacing d(001). We develop a model that rationalizes the size of the interlayer spacing in terms of intralayer shifts of the pentacene molecules along their long molecular axes.