International Journal of Modern Physics B

A geometrical approach is constructed to explain the dependence of lattice thermal conductivity (LTC) in InAs/GaAs multi-layered superlattice structures (SLs). The Morelli–Callaway model is applied to calculate the LTC of InAs/GaAs SLs with the assumption of InAs+GaAs thickness as a grain boundary and the total layer thickness as the sample size. Calculations gave a systematically conventional temperature dependence of LTC for nine different samples depending on their number of layers and the InAs and GaAs layer thicknesses having their ratio from 0.13 to 0.295. The dependence of LTC for both peak values at the low and room temperature were examined according to sample size, number of layers and layer thickness ratio. A new relation is examined for the assessment of the grain boundary effects. The best dependence of LTC was obtained by introducing the effects of the layer thickness ratio (InAs/GaAs) and the sample size D in the form [D/(InAs/GaAs)] which gave a systematic mathematical fitting equation.

This paper presents a simulation of the structural and optoelectronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) compounds. Theoretical modeling was performed using ab initio first-principles calculations, specifically the density functional theory (DFT), and the Mindlab numerical software. The software used two methods: the full-potential muffin-tin orbital method (FP-LMTO) and the full-potential plane-wave method (FP-LAPW). These two methods are employed to solve the Schrödinger equation. The exchange correlation effects have been computed using two different approximations: the generalized gradient approximation (GGA) and the local density approximation (LDA). Our findings indicate that the zinc blende structure (B3) is the stable phase, while the Wurtzite phase (B4) is metastable for the AlAs compound. On the other hand, the ScAs compound crystallizes in the NaCl phase (B1). The AlAs compounds undergo three phase transitions: $\mathrm{\text{B3}}\to \mathrm{\text{B4}}$, $\mathrm{\text{B3}}\to \mathrm{\text{B2}}$ and $\mathrm{\text{B3}}\to \mathrm{\text{B1}}$. In contrast, ScAs does not undergo any transition. The obtained results for equilibrium energies, lattice parameters and gap energies are in closer agreement with the experimental and theoretical data. The AlAs compound exhibits a semiconducting character, while ScAs exhibits a semi-metallic character. Additionally, the refractive index of these two compounds is similar to that of silicon, which is crucial for their application in photovoltaic cells.

The dimension of the Hilbert space needed for the description of an interacting electron system increases exponentially with electron number N. As pointed out by Kohn this exponential wall problem (EWP) limits the concept of many-electron wavefunctions based on solutions of Schrödinger’s equation to $N\le N_0$, where $N_0\approx 10^3$ [Rev. Mod. Phys. 71, 1253 (1999)]. This limitation does not hold when the electronic interactions are neglected or treated in a mean-field approximation. The EWP has directed electronic structure calculations for solids to methods like density-functional theory which avoid dealing with many-electron wavefunctions. We show that the highly unsatisfactory limitation of many-electron wavefunctions to $N\le N_0$ can be overcome by generalizing their definition. We show for the ground state of a large system that it is the logarithm of the solution of Schrödinger’s equation which should be used to characterize this system. In this case the wavefunctions of independent subsystems add up rather than multiply. This feature is realized by the action function. It provides a simple physical picture for the resolution of the EWP.

I discuss the sharp dissonance between the recent Nature Materials Editorial “Trust but verify” [Nature Materials Editorial, Nat. Mater. 23, 1 (2024)] and the publication, in the same journal issue, of the Feature Comment by M. I. Eremets and coauthors on hydride superconductivity [M. I. Eremets et al., Nat. Mater. 23, 26 (2024)].

In this paper, electronic properties of Janus MSX monolayers (M = Mo, W; X = Se or Te), including electron energy loss near edge structures (ELNES), as K and $L_{2,3}$ edge spectra of sulfur atoms, have been calculated using a full potential scheme and the augmented plane wave plus local orbitals (APW+lo) method in the framework of density functional theory (DFT). Due to the lack of experimental results, the obtained spectra are compared with the corresponding spectra of MoS₂ monolayer. The band structure analysis shows that the Janus MoSSe and WSSe monolayers are direct bandgap semiconductors, while the Janus MoSTe and WSTe monolayers are indirect bandgap semiconductors. In comparison to MoS₂, the main structures of the K edge ELNES spectra of sulfur atoms in Janus monolayers occur at lower energies, due to the structural change and increased bond length. The relative reduction of intensities in the main structures predicts the possibility of reducing the number of partial densities of states (PDOS), that is, the reduced p PDOS for the K edge in the corresponding energy range. In the K ($L_{2,3})$ edge ELNES spectra of the sulfur atom in Janus monolayers and MoS₂ monolayers, the main structures are due to the electron transfer to the unoccupied $p_x+p_y$ and $p_z$ states (3s of sulfur and 4d states of the transition metal).

DFT studies are performed to investigate the crystal structure and geometry, electronic and magnetic properties of brownmillerite-type strontium-based oxygen-deficient perovskites ${\text{SrTMO}}_{2.5}$ (TM = Mn, Fe, Co and Cu) in orthorhombic phase. The comparison of the calculated lattice parameters shows consistency with the experiments, and all these perovskites are thermodynamically stable as revealed by cohesive energy. The spin-dependent calculations of the electronic band profiles demonstrate the metallic behavior of all these deficient perovskites. The increase in electrical resistivity and electronic thermal conductivities with temperature also confirms the metallic behavior of these compounds. The optimized ground state energies in different magnetic phases and post-DFT treatment confirm that ${\text{SrMnO}}_{2.5}$ and ${\text{SrCoO}}_{2.5}$ are stable in C-type AFM, ${\text{SrFeO}}_{2.5}$ is in G-type AFM and ${\text{SrCuO}}_{2.5}$ in A-type AFM phase, respectively. The high specific heat of these deficient perovskites makes them good candidates for high-temperature technology. Based on the above physical properties, it is expected that these deficient perovskites are potential candidates for spintronics and magnetic storage devices.

The effect of 2MeV energy electrons with fluences from $0.5\times 10^{17}$ to $4.0\times 10^{17}$ electron/cm² on the crystal structure, surface morphology, absorption spectrum, band gap, Raman spectrum and microhardness of ZnS crystal was investigated. The crystal structure of ZnS is face-centered cubic with space group F-43m. Upon irradiation with a fluence of $4\times 10^{17}$ electron/cm², the unit cell parameter decreased by 0.0195Å, and the coordinates of the Zn${}^{+2}$ ions were changed. Irradiation with fluences ranging from $0.5\times 10^{17}$ to $4\times 10^{17}$ electron/cm² increased crystallite size from 20nm to 28nm. The study of the surface morphology of the ZnS single-crystal revealed that irradiation caused a reduction in both the width ($R_a$) and height ($R_z$) of the surface roughness. The band gap of the ZnS single-crystal decreased from 3.521 to 3.506eV when irradiated with fluence electrons from $0.5\times 10^{17}$ to $2.5\times 10^{17}$electron/cm². Raman spectrum observations showed an increase in the longitudinal optical (LO) mode peak (350cm${}^{-1}$) intensity following the irradiation of ZnS single-crystal with electrons. The microhardness of the ZnS single-crystal showed an exponential increase by 20% when irradiated with fluences from $0.5\times 10^{17}$ to $2.5\times 10^{17}$electron/cm².

The influence of pure solvent and binary solvent mixtures on the optical properties of non-steroidal anti-inflammatory drug (NSAID) molecule, specifically flufenamic acid (FLA), has been studied using absorption and fluorescence spectroscopic techniques. A bathochromic shift is observed in the emission wavelength of FLA with an increase in the solvent polarity of pure solvents, attributed to the highest stability of the excited state. The spectral properties are correlated with Lippert–Mataga, solvent polarity parameter, Kamlet, and Catalan solvent polarity parameters, suggesting that both general and specific solvent effects influence the spectral properties, with general solvent effects dominating over specific solvent effects. Preferential solvation studies have been carried out in tetrahydrofuran (THF) and water solvent mixture, revealing variations in the preference for solvation of FLA as a function of the mole fraction of water. Solvatochromic data are utilized to estimate the excited state dipole moment in pure solvents using different solvatochromic methods, revealing that the excited state dipole moment of FLA is higher than its ground state counterpart. The increase in dipole moment in the excited state compared to the ground state is explained based on intramolecular charge transfer (ICT), with elaboration and discussion on the possible resonance structure corresponding to ICT, inferring the more polar nature of the excited state compared to the ground state. The effect of solute polarizability on the excited state dipole moment and change in dipole moment is also discussed.

The carbon is an important element which belongs to group 14 of the periodic table and shows multiple applications in our daily life as well as at the industrial scale. It is a promising element which represents the liquid–liquid phase transition (LLPT) phenomena. Additionally, it shows interesting anomalous behavior with some usual thermodynamic properties such as heat capacity ($C_p$) near about the liquid–liquid phase coexistence temperature ($T_c$). Hence, it is quite challenging and difficult to simulate carbon at or near the liquid–liquid phase coexistence temperature. This anomalous behavior also creates complications in computing the precise and equilibrated thermodynamic properties close to $T_c$. Therefore, we have studied the thermodynamic behavior of liquid and solid (diamond) states of carbon at liquid–liquid phase coexistence temperature ($T_c$) while transforming from liquid to solid state and achieving the equilibrated liquid and solid states individually. Additionally, we have also performed a similar analysis on melting temperature ($T_m$) to compare the system trends and its thermodynamics behavior in liquid and solid states, respectively. Furthermore, all the predicted thermodynamic results are quite consistent and able to show the equilibrium changes at the liquid–liquid phase coexistence temperature ($T_c$) and melting temperature ($T_m$), respectively.

The emergence of Majorana fermion bound states has been studied in several environments. In this paper, we discuss the current-voltage characteristics of a Majorana fermion state as a function of the voltage, temperature, and magnetic field and compare the results to experiment. Based on the agreement and identified parameters, we calculate the noise as possible proof of the emergence of Majorana fermions.

The Ni-doped CdSe nanostructured thin films during the deposition procedure that govern the altering of the optical transitions have been investigated. The concentration of Ni as doping inside CdSe from 0.01, 0.02 to 0.03mol in the form of nanostructured thin layers have been fabricated through a simple chemical solution deposition approach. Doping of the Ni to CdSe adds the new transitions related to NiSe, which means the tiny concentration of Ni ions creates the new transition to CdSe that sample has multiple optical bandgaps. There is an order in band gap changing with doping concentration raising so that increasing the Ni${}^{2+}$ ions decreases the optical band gap to 1.59eV although the optical band gap for CdSe in bulk state is 1.74eV, so doping procedure decreases optical bandgap of CdSe that is mean doping procedure creates the new structure. It has shown that it’s possible to determine the Urbach energy of the samples from the absorption spectrum without the need to determine the adsorption coefficient from the determination of thickness. Degradation efficiency for pure CdSe is 86% while a sample of Ni-doped CdSe enhanced degradation efficiency until 93%.

Recently, graphyne-based gas sensors have drawn a lot of interest. One kind of graphene with acetylene bonds connecting its hexagons is graphyne. In this study, the density functional theory (DFT) method was used to investigate the physical parameters of the surface adsorption of carbon monoxide on the $\alpha$- and $\gamma$-graphyne nanosheet, taking into account van der Waals (vdW) interactions through the use of the SIESTA computational code. CO molecule adsorbed and optimized in two vertical and horizontal states from the side of carbon and oxygen atoms, at different distances and sites relative to the graphyne sheet. After optimization and finding the adsorption energy, the best adsorption sites, equilibrium distance of the molecule from the surface, electronic structure, charge transfer rate, and bandgap changes were calculated. It was observed that the changes in the electronic structure after the adsorption of CO molecule are insignificant and the $\alpha$- and $\gamma$-graphyne nanosheets remained zero-gap and narrow-gap semiconductors, respectively. The adsorption of CO molecule on the $\alpha$- and $\gamma$-graphyne nanosheets is physisorption. The results show that the $\gamma$-graphyne nanosheet has a good potential for adsorbing and detecting CO molecules and sensor applications.