The study of photoexcitations in molecular aggregates faces the twofold problem of the increased computational cost associated with excited states and the complexity of the interactions among the constituent monomers. A mechanistic investigation of these processes requires the analysis of the intermolecular interactions, the effect of the environment, and 3D arrangements or crystal packing on the excited states. A considerable number of techniques have been tailored to navigate these obstacles; however, they are usually restricted to in‐house codes and thus require a disproportionate effort to adopt by researchers approaching the field. Herein, we present the FRamewOrk for Molecular AGgregate Excitations (fromage), which implements a collection of such techniques in a Python library complemented with ready‐to‐use scripts. The program structure is presented and the principal features available to the user are described: geometrical analysis, exciton characterization, and a variety of ONIOM schemes. Each is illustrated by examples of diverse organic molecules in condensed phase settings. The program is available at https://github.com/Crespo-Otero-group/fromage.

A geometric analysis of the cubic A2BX6 structure commonly formed by metal halides is presented. Using the 'hard sphere' approximation, where the ions are represented by spheres of a fixed radius, we derive four limiting models that each constrain the distances between constituent ions in different ways. We compare the lattice parameters predicted by these four models with experimental data from the Inorganic Crystal Structure Database (ICSD). For the fluorides, the maintenance of the AX bond length at the sum of the A and X radii gives the best approximation of the lattice parameter, leading to structures with widely separated BX6 octahedra. For the heavier halides, a balance between forming an A site cavity of the correct size, and maintaining suitable anion-anion distances determines the lattice parameter. It is found that in many A2BX6 compounds of heavier halides, the neighbouring octahedra show very significant anion-anion overlap. We use these models to predict a compound with A site rattling and use DFT to confirm this prediction. Lastly, we use the geometric models to derive formability criteria for vacancy ordered double perovskites.

Using ab initio methods, we predict α-Bi2Sn2O7 to have an ultra-low lattice thermal conductivity at room temperature due to the high density of phonon scattering events, which makes it a potential earth-abundant n-type low temperature thermoelectric.

Accurately modelling polymorphism in crystalline solids remains a key challenge in computational chemistry. In this work, we apply a theoretically-rigorous phonon mode-mapping approach to understand the polymorphism in the ternary...

We report the successful electrochemical intercalation of F-ions into a densely packed perovskite oxide from a liquid electrolyte at room temperature. Using galvanostatic oxidation and electrochemical impedance spectroscopy coupled with operando X-ray diffraction, we show that roughly 0.5 equivalents of F-ions can be inserted onto the vacant A-site of the perovskite ReO3. Density functional theory calculations indicate that the intercalated phase is thermodynamically unfavorable compared to other less densely packed polymorphs of ReO3F. Pairing X-ray spectroscopy, neutron total scattering measurements, and magic-angle spinning 19F NMR confirms a rapid decomposition of the product on removal from the cell but nevertheless, these results clearly demonstrate that small anions like fluoride can be intercalated into solids as readily as alkali cations at room temperature, which opens new opportunities to electrochemically fluorinate many new materials. File list (2)download file view on ChemRxiv FxReO3.pdf (12.07 MiB) download file view on ChemRxiv supporting_information.pdf (5.70 MiB)

Reducing the thickness of a material to its two-dimensional (2D) limit can have dramatic consequences for its collective electronic states, including magnetism, superconductivity, and charge and spin ordering. An extreme case is TiTe2, where a charge density wave (CDW) emerges in the single-layer, which is absent for the bulk compound, and whose origin is still poorly understood. Here, we investigate the electronic band structure evolution across this CDW transition using temperature-dependent angle-resolved photoemission spectroscopy. Our study reveals an orbital-selective band hybridisation between the backfolded conduction and valence bands occurring at the CDW phase transition, which in turn leads to a significant electronic energy gain, underpinning the CDW transition. For the bulk compound, we show how this energy gain is almost completely suppressed due to the three-dimensionality of the electronic band structure, including via a kz-dependent band inversion which switches the orbital character of the valence states. Our study thus sheds new light on how control of the electronic dimensionality can be used to trigger the emergence of new collective states in 2D materials.

The environmental burden of fossil fuels and the rising impact of global warming have created an urgent need for sustainable clean energy sources. This has led to widespread interest in...

<p>The study of photoexcitations in molecular aggregates faces the twofold problem of the increased computational cost associated with excited states and the complexity of the interactions among the constituent monomers. A mechanistic investigation of these processes requires the analysis of the intermolecular interactions, the effect of the environment, and 3D arrangements or crystal packing on the excited states. A considerable number of techniques have been tailored to navigate these obstacles, however they are usually restricted to in-house codes and thus require a disproportionate effort to adopt by researchers approaching the field. Herein we present the FRamewOrk for Molecular AGgregate Excitations (fromage), which implements a collection of such techniques in a Python library complemented with ready-to-use scripts. The program structure is presented and the principal features available to the user are described: geometrical analysis, exciton characterisation and a variety of ONIOM schemes. Each is illustrated by examples of diverse organic molecules in condensed phase settings. The program is available at https://github.com/Crespo-Otero-group/fromage.</p>