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Zintl materials have received enormous attention in recent time due to their unique structure and thermoelectric efficiency. In this work, quaternary Zintl compounds LaAgZnX2 (X = P, As) have been comprehensively investigated using the FP-LAPW + lo method through first principles approximation. The dynamic stability of the samples is performed through phonon analysis. Birch–Murnaghan equation of states is used to determine ground state parameters. The lattice constant increases while formation energy and bulk modulus B(GPa) decrease by anion replacement from P to As. Band structure calculation shows that LaAgZnP2 is an indirect bandgap semiconductor while LaAgZnAs2 is a direct bandgap semiconductor. The density of states (DOS) demonstrates that the valence band (V.B) is mainly comprised of Zn-d and X-p states while the La-f state is in the conduction band (C.B) along with the minor contribution of the La-d state. Substantial absorption is observed in the low-frequency ultraviolet and visible spectrums for these compounds. Red shifting of the hallmark optic peak occurs due to the anion replacement from P to As. To investigate the electric and thermal conductivities, Seebeck coefficients, and thermopower factor, the Boltzmann transport theory is used to quantify them for these materials. High absorption peaks and figures of merits of these compounds highlight their potential usage in optoelectronics and thermoelectric systems. [ABSTRACT FROM AUTHOR]

First-principles calculations based on density-functional theory have been used to investigate the effect of biaxial strain and oxygen vacancy on the electronic, photocatalytic, and electrocatalytic properties of PbTiO3 oxide. Our results show that PbTiO3 has a high exciton binding energy and a band gap that can be easily moderated with different strain regimes. From a reactivity viewpoint, the highly exothermic adsorption of hydrogen atoms in both pristine and strained PbTiO3 structures does not make it a potential electrocatalyst for the hydrogen evolution reaction. Fortunately, the presence of oxygen vacancies on the PbTiO3 surface induces moderate adsorption energies, making the reduced PbTiO3 suitable for hydrogen evolution reaction processes. [ABSTRACT FROM AUTHOR]

Using density-functional theory calculations, we determined the pressure domain of stability of beryllium metasilicate, BeSiO 3 , an elusive compound for which no stable polymorph is known until now. We found that BeSiO 3 is stable at pressures above 9 GPa, a condition that makes it accessible with a large-volume press. After considering the cubic, orthorhombic, and hexagonal perovskite structures and the Ilmenite structure, known from related compounds, we propose that the most stable structure among them is the orthorhombic perovskite structure described by space group Pnma . The unit-cell parameters of this structure are a = 4.966 Å, b = 7.160 Å, and c = 4.374 Å. We also determined the frequencies of Raman and infrared phonons, the elastic constants and modulus, and the electronic band structure for the orthorhombic perovskite structure. Finally, the pressure dependence of unit-cell parameters was calculated. Compression was found to be slightly anisotropic, with the axial compressibilities decreasing following the sequence κ b > κ c > κ a . In addition, we found that BeSiO 3 is quite incompressible with a bulk modulus of 242 GPa, which makes it one of the less compressible silicates. To understand, such a large bulk modulus, both the quantum theory of atoms in molecules and the electron localization function decomposition were utilized to analyze the bonding and to relate it to the mechanical properties.

Finding green energy resources that contribute to the battle against global warming and the pollution of our planet is an urgent challenge. Thermoelectric electricity production is a clean and efficient method of producing energy; consequently, scientists are currently researching and creating thermoelectric materials to increase the efficiency of thermoelectric electricity production and expand the potential of the thermoelectric effect for clean energy production. This work focuses on a comprehensive study of the thermoelectric properties of two-dimensional ScYCBr 2 . We report here a computational analysis of this Janus-like MXene, which is predicted to exhibit outstanding thermoelectric properties. The study uses density-functional theory to provide evidence of the important role played by symmetry breaking to promote low-thermal transport by favoring certain phonon scattering channels. Compared to its symmetric parent compounds, the asymmetric Janus-type ScYCBr 2 displays additional phonon scattering channels reducing the thermal conductivity. An exhaustive investigation of the dynamical stability for both zero-temperature and high-temperature conditions was also performed to support the stability of ScYCBr 2 . Our analysis shows that thanks to its asymmetric structure, the ScYCBr 2 MXene has thermoelectric properties that largely surpass those of its parent symmetric counterpart Sc 2 CBr 2 , being a material with a remarkable thermoelectric high figure of merit. Another advantage of ScYCBr 2 is its high carrier mobility. This work not only demonstrates that this material is a promising thermoelectric material but also shows that ScYCBr 2 can operate efficiently at high temperatures up to 1200 K., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

We report a computational study where we explore the possibility of tuning the electronic properties of orthorhombic methylammonium tin iodide CH 3 NH 3 SnI 3 using strains. According to our findings, a moderate [001] strain, smaller than 2%, would open the band gap up to 1.25 eV and enhance the exciton binding energy, opening up new possibilities for the use of CH 3 NH 3 SnI 3 in technological applications. To better understand the impact of strain, we also examined its influence on bonding properties. The results reveal that the directional pnictogen and the hydrogen bonding are not altered by strains and that the tuning of the electronic properties is the result of changes induced in the orbital contributions to states near the Fermi level and the tilting of the SnI 6 octahedral units., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

Identifying and evaluating novel and extremely stable materials for catalysis is one of the major challenges that mankind faces today to rapidly reduce the dependence on fossil fuels. To contribute to achieving this goal, we have evaluated within the density-functional framework the properties of a new two-dimensional MXene structure, the asymmetric MXene YZrCOF monolayer. Phonon dispersion calculations at 0 K and 300 K indicate that the studied material is dynamically stable. The calculations also indicate that the material has a rigid crystal structure with a wide band gap, a strong potential difference, and a band-gap alignment that favors the production of both H 2 and O 2 molecules from water splitting. We also report the outcome of the strain effect on the electrical and photocatalytic characteristics of the studied material. We will demonstrate that even under a large strain, the YZrCOF monolayer is stable and useful for photocatalytic applications.

The discovery of novel materials for catalytic purposes that are highly stable is one of the main challenges nowadays for reducing our dependence on fossil fuels. Here, low-dimensional PbTiO 3 is introduced as an electrocatalyst using first-principles calculations. Density-functional theory calculations indicate that 2D-PbTiO 3 is dynamically and thermodynamically stable. Our results show that a single oxygen defect vacancy in 2D-PbTiO 3 can play a key role in enhancing the hydrogen evolution reaction (HER), together with the Ti atoms. Our study concludes that the Volmer-Heyrovsky mechanism is a more favorable route to achieve HER than the Volmer-Tafel mechanism, including solvation and vacuum conditions.

First-principles calculations based on density-functional theory have been used to investigate the effect of biaxial strain and oxygen vacancy on the electronic, photocatalytic, and electrocatalytic properties of PbTiO 3 oxide. Our results show that PbTiO 3 has a high exciton binding energy and a band gap that can be easily moderated with different strain regimes. From a reactivity viewpoint, the highly exothermic adsorption of hydrogen atoms in both pristine and strained PbTiO 3 structures does not make it a potential electrocatalyst for the hydrogen evolution reaction. Fortunately, the presence of oxygen vacancies on the PbTiO 3 surface induces moderate adsorption energies, making the reduced PbTiO 3 suitable for hydrogen evolution reaction processes.

We present for the first time a theoretical study of the structural stability and physical properties of the newly synthesized Ag 2 WS 4 . The study contributes to a better understanding of its electronic and vibrational properties, which is fundamental for the optimization of the technological applications of Ag 2 WS 4 . Calculations have been carried out by means of density-functional theory. The obtained results support that Ag 2 WS 4 is thermodynamically, mechanically, and dynamically stable in a tetragonal layered structure, in good agreement with experiments. Calculations have also been used to obtain phonon frequencies, their assignments, and the Raman scattering spectrum. Furthermore, we show that Ag 2 WS 4 has a brittle structure, that is governed by van der Waals interactions, which favors its exfoliation as a low-dimensional structure. Additionally, the results show that Ag 2 WS 4 has a band gap of 2.02 eV with a favorable band-edge diagram for water splitting as well as for optoelectronic applications., (© 2022 IOP Publishing Ltd.)

The study of novel two-dimensional structures for potential applications in photocatalysis or in optoelectronics is a challenging task. In this work, first-principles calculations have been carried out to explore the properties of the two-dimensional perovskite-based MgPSe 3 . Dynamic and mechanical analyses confirm the stability of this low-dimensional material. Our calculated Raman frequencies are in good agreement with previous studies. Furthermore, a topological bonding analysis, based on the electron localization function, indicates a covalent and ionic character for the P-Se and Mg-Se bonds, respectively. From a reactivity point of view, water interacts poorly with MgPSe 3 and its associative interaction is physisorbed and governed by weak interactions. Consequently, the low dissociative energy of H 2 O molecules affects the reaction taking place on the surface of the material, making it unfavorable for both hydrogen and oxygen evolution reactions. However, the computed electronic properties show that MgPSe 3 is a promising material for optoelectronic applications.

A computational study was carried out to investigate the effect of surface termination on Janus Hf 2 COS MXene by substituting partly the O-terminated layer with S atoms. Our predictions confirm that this chemical strategy allows one to tailor the band gap of MXenes. Indeed, the semiconducting character of Hf 2 CO 2 MXene decreases by the exchange of O by S atoms. From a structural point of view, dynamical, mechanical, and thermal analysis confirm the thermodynamic stability of the Janus Hf 2 COS MXene, which shows metallic character. Furthermore, topological chemical analysis indicates an ionic nature of Hf 2 CO 2 MXene that tends to be reduced by increasing the concentration of S atoms, promoting a covalent character. Shortly, the present study illustrates how the properties of MXenes can be tailored by functionalizing them with different chemical terminations.

In this study, the effect of nitrogen substitution in wolframite-type ScTaO 4 was investigated using density-functional theory calculations. First, structural and mechanical properties, as well as the dynamical stability of ScTaO 4 were examined deeply for the ambient-pressure structure. Subsequently, we studied how lattice vibrations are affected by hydrostatic pressure and determined the elastic moduli of ScTaO 4 . The results of our study show that the monoclinic structure of ScTaO 4 is rigid and non-compressible. In addition, band-structure calculations show that ScTaO 4 has a wide direct band-gap of 4.04 eV, which in turn leads to a possible tuning of electronic properties. We have found that this task can be conducted by partially substituting oxygen atoms in the unit cell with nitrogen atoms. Both band-structure calculations and charge-density analyses revealed a narrowing in the band gap caused by the presence of nitrogen atoms, which act as a shallow acceptor state, resulting in weak repulsive interactions and structural distortions in both Sc and Ta coordination polyhedra; reducing the crystal symmetry from monoclinic to triclinic.