Crystal structure and electronic properties of low-dimensional hexamethylenediaminium lead halide perovskites.

This work reports on hybrid hexamethylenediaminium lead halide perovskites. The materials were prepared using wet synthesis and the subsequent precipitation from aqueous solution. Structural and morphological charactarization studies show their high degree of crystallinity and phase purity.

Crystal and Electronic Structures of New Two Dimensional 3-NH-PyPbX Haloplumbate Materials.

In this study, we explored both the crystal and electronic structures of new synthesized materials 3-NH-PyPbX (X = Br, I). Both compounds are isostructural, and they crystallize in the monoclinic space group 2/, with four formula units in the unit cell. According to the analysis of their electronic structures, both compounds are direct semiconductors with direct transitions between valence and conduction bands occurring at the -points A, Z, and at about half of the distance between the -points D/D1 and D1/E.

Effective Method for the Determination of the Unit Cell Parameters of New MXenes.

MXenes are of great practical interest. While the physical properties of such a well-known MAX phase as TiAlC and the TiC MXene that is based on it have been widely studied, it is extremely important to study the properties of new four-component MAX-phases and the MXenes based on them. To do this, first, it is necessary to characterize the obtained materials.

Revisiting the BaBiO semiconductor photocatalyst: synthesis, characterization, electronic structure, and photocatalytic activity.

This article revisits the properties of BaBiO examined extensively in the last two decades because of its electronic properties as a superconductor and as a semiconductor photocatalyst. Solid-state syntheses of this bismuthate have often involved BaCO as the barium source, which may lead to the formation of BaBiO/BaCO heterostructures that could have an impact on the electronic properties and, more importantly, on the photocatalytic activity of this bismuthate. Accordingly, we synthesized BaBiO by a solid-state route to avoid the use of a carbonate; it was characterized by XRD, SEM, and EDX, while elemental mapping characterized the composition and the morphology of the crystalline BaBiO and its thin films with respect to structure, optoelectronic, and photocatalytic properties.

Synthesis, characterization, optoelectronic and photocatalytic properties of SrBiO/SrCO and SrBiO/SrCO heterostructures with varying SrCO content.

We report on the structure and properties of novel SrBiO/SrCO and SrBiO/SrCO heterostructures with SrCO content varying from 10 wt% to 90 wt%. Formation of the heterostructures is succeeded via sintering technique and according to XRD, SEM, and EDX studies has resulted in highly crystalline materials with well-defined carbonate-bismuthate interfaces. In the reaction of photodegradation of phenol in aqueous solution the heterostructures demonstrated photocatalytic activity exceeding that of TiO.

Effect of Composition on the Optical and Photocatalytic Properties of Visible Light Responsive Materials BiMgO.

We report the synthesis and the crystal and electronic structure as well as the optical and photocatalytic properties of novel photoactive materials of the general formula BiMgO. Two compounds with compositions of BiMgO and BiMgO are synthesized using the pyrolytic method. According to X-ray diffraction analysis, the materials are monocrystalline species.

The effect of organic cations on the electronic, optical and luminescence properties of 1D piperidinium, pyridinium, and 3-hydroxypyridinium lead trihalides.

We present a structural and optoelectronic study of 1D piperidinium, pyridinium, and 3-hydroxypyridinium lead trihalides. In contrast to the piperidinium and pyridinium species whose single inorganic chains [PbX31-]n are separated by organic cations, the 3-hydroxypyridinium compound is characterized by double inorganic chains. According to DFT the valence and conduction bands of the piperidinium lead trihalides are composed of occupied p-orbitals of the halogen anions and unoccupied p-orbitals of the Pb2+ cations.

Ab Initio Insight into Mechanisms of Ozone Interaction with a Surface of Dehydrated Nanocrystalline TiO.

Density functional theory (DFT) study of ozone adsorption on dehydrated nanocrystalline TiO is presented. Singlet and triplet binding modes of ozone to the oxide's titanium cations are considered. In both the modes, monodentate and bidentate ozone complexes are formed.

Pyridinium lead tribromide and pyridinium lead triiodide: quasi-one-dimensional perovskites with an optically active aromatic π-system.

Two novel hybrid organic-inorganic perovskites, pyridinium lead tribromide and pyridinium lead triiodide, are prepared. Based on the XRD data, we find that the compounds are quasi-one-dimensional crystals of Pna21 symmetry. DFT calculations demonstrate that the valence band of the new compounds is comprised of the occupied p-orbitals of the halogen anions, while their conduction bands CB and CB + 1 are composed mainly of the unoccupied π-orbitals of the aromatic pyridinium rings.

Low Inhomogeneous Broadening of Excitonic Resonance in MAPbBr Single Crystals.

We present an optical study of MAPbBr single crystal grown from solution. The crystal Pm3m symmetry was confirmed by electron backscatter diffraction. Our major attention was focused on optical effects related to the excitonic states in MAPbBr.

Photoionisation study of Xe.CF4 and Kr.CF4 van-der-Waals molecules.

We report on photoionization studies of Xe.CF4 and Kr.CF4 van-der-Waals complexes produced in a supersonic expansion and detected using synchrotron radiation and photoelectron-photoion coincidence techniques.

FDE-vdW: A van der Waals inclusive subsystem density-functional theory.

We present a formally exact van der Waals inclusive electronic structure theory, called FDE-vdW, based on the Frozen Density Embedding formulation of subsystem Density-Functional Theory. In subsystem DFT, the energy functional is composed of subsystem additive and non-additive terms. We show that an appropriate definition of the long-range correlation energy is given by the value of the non-additive correlation functional.

Self-assembled organic nanowires for high power density lithium ion batteries.

The electroactive organic materials are promising alternatives to inorganic electrode materials for the new generation of green Li-ion batteries due to their sustainability, environmental benignity, and low cost. Croconic acid disodium salt (CADS) was used as Li-ion battery electrode, and CADS organic wires with different diameters were fabricated through a facile synthetic route using antisolvent crystallization method to overcome the challenges of low electronic conductivity of CADS and lithiation induced strain. The CADS nanowire exhibits much better electrochemical performance than its crystal bulk material and microwire counterpart.

Calculating hyperfine couplings in large ionic crystals containing hundreds of QM atoms: subsystem DFT is the key.

We present an application of the linear scaling frozen density embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfcc's) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems range from an isolated guanine to a 15,000 atom QM/MM cluster where the QM region is comprised of 36 protonated guanine cations, 36 chlorine anions, and 42 water molecules. Our calculations show that the embedding effects of the surrounding crystal cannot be reproduced by small model systems nor by a pure QM/MM procedure.

Interaction between n-Alkane Chains: Applicability of the Empirically Corrected Density Functional Theory for Van der Waals Complexes.

The geometries, interaction energies, and vibrational frequencies of a series of n-alkane dimers up to dodecane have been calculated using density functional theory (DFT) augmented with an empirical dispersion energy term (DFT-D). The results obtained from this method for ethane to hexane dimers are compared with those provided by the MP2 level of theory and the combined Gaussian-3 approach with CCSD(T) being the highest correlation method [G3(CCSD(T))]. Two types of dimer isomers have been studied.

Interaction energies in hydrogen-bonded systems: a testing ground for subsystem formulation of density-functional theory.

The formalism based on the total energy bifunctional (E[rhoI,rhoII]) is used to derive interaction energies for several hydrogen-bonded complexes (water dimer, HCN-HF, H2CO-H2O, and MeOH-H2O). Benchmark ab initio data taken from the literature were used as a reference in the assessment of the performance of gradient-free [local density approximation (LDA)] and gradient-dependent [generalized gradient approximation (GGA)] approximations to the exchange-correlation and nonadditive kinetic-energy components of E[rhoI,rhoII]. On average, LDA performs better than GGA.