Light absorption capability and electronic band structure are both fundamental information for the development of a new photocatalyst. Here, we investigated two oxyfluoride photocatalysts Pb 2 Ti 4 O 9 F 2 and Pb 2 Ti 2 O 5.4 F 1.2 , which were active for H 2 evolution in the presence of a sacrificial reagent, by means of X-ray diffraction, UV−visible diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, and density functional theory calculations. Pb 2 Ti 4 O 9 F 2 and Pb 2 Ti 2 O 5.4 F 1.2 show absorption edges at around 410 and 510 nm, respectively, corresponding to band gaps of 3.0 and 2.4 eV. The different band gap values of the two materials are mainly due to their valence band maximum (VBM); the VBM of Pb 2 Ti 4 O 9 F 2 is positioned at approximately 0.9 V more positive than that of Pb 2 Ti 2 O 5.4 F 1.2 . The significantly different VBM positions in these oxyfluorides could be explained in terms of the orbital interaction between Pb 6s/6p and O 2p in the valence band, where the shorter Pb−O bond in Pb 2 Ti 2 O 5.4 F 1.2 reinforced the interaction, leading to more elevated VBM and a narrower band gap.

A clustering technique is applied using dynamic‐time‐wrapping (DTW) analysis to X‐ray diffraction (XRD) spectrum patterns in order to identify the microscopic structures of substituents introduced into the main phase of magnetic alloys. The clustering technique is found to perform well, identifying the concentrations of the substituents with success rates of ≈90%. This level of performance is attributed to the capability of DTW processing to filter out irrelevant information such as the peak intensities (due to the uncontrollability of diffraction conditions in polycrystalline samples) and the uniform shift of peak positions (due to the thermal expansion of lattices). The established framework is not limited to the system treated in this work, but is widely applicable to systems the properties of which are to be tuned by atomic substitutions within a phase. The framework has a broader potential to predict properties such as magnetic moments, optical spectra etc.) from observed XRD patterns, by predicting such properties evaluated from predicted microscopic local structure.

Lattice thermal conductivities (LTC) for a subset of polymer crystals from the Polymer Genome Library were investigated to explore high LTC polymer systems. We employed a first-principles approach to evaluating phonon lifetimes within the third-order perturbation theory combined with density functional theory, and then solved the linearized Boltzmann transport equation with single-mode relaxation time approximated by the computed lifetime. Typical high LTC polymer systems, polyethylene (PE) crystal and fiber, were benchmarked, which is reasonably consistent with previous references, validating our approach. We then applied it to not only typical polymer crystals, but also some selected ones having structural similarities to PE. Among the latter crystals, we discovered that beta phase of Poly(vinylidenesurely fluoride) (PVF-β) crystal has higher LTC than PE at low temperature. Our detailed mode analysis revealed that the phonon lifetime of PVF-β is more locally distributed around lower frequency modes and four-times larger than that of PE. It was also found from a simple data analysis that the LTC relatively correlates with curvature of energy-volume plot. The curvature would be used as a descriptor for further exploration of high LTC polymer crystals by means of a data-driven approach beyond human-based one.

No abstract

A common approach for studying a solid solution or disordered system within a periodic ab initio framework is to create a supercell in which certain amounts of target elements are substituted with other elements. The key to generating supercells is determining how to eliminate symmetry-equivalent structures from many substitution patterns. Although the total number of substitutions is on the order of trillions, only symmetry-inequivalent atomic substitution patterns need to be identified, and their number is far smaller than the total. Our developed Python software package, which is called Shry (Suite for High-throughput generation of models with atomic substitutions implemented by Python), allows the selection of only symmetry-inequivalent structures from the vast number of candidates based on the canonical augmentation algorithm. Shry is implemented in Python 3 and uses the CIF format as the standard for both reading and writing the reference and generated sets of substituted structures. Shry can be integrated into another Python program as a module or can be used as a stand-alone program. The implementation was verified through a comparison with other codes with the same functionality, based on the total numbers of symmetry-inequivalent structures, and also on the equivalencies of the output structures themselves. The provided crystal structure data used for the verification are expected to be useful for benchmarking other codes and also developing new algorithms in the future.