Halide perovskites have emerged as a transformative class of materials for optoelectronic and energy-harvesting applications owing to their outstanding photophysical properties and tunable electronic structures. However, the widespread adoption of lead-based perovskites is hindered by concerns over their toxicity and environmental instability, driving the search for eco-friendly and stable alternatives. In this context, fluoride-based double perovskites represent a promising avenue due to their enhanced chemical stability and suitability for ultraviolet (UV) optoelectronics and thermoelectric devices. This work presents the first comprehensive first-principles investigation of the structural stability, optoelectronic behaviour, and thermoelectric performance of the novel lead-free fluoride double perovskite Rb2AlAgF6 compound. Density functional theory (DFT) calculations, supported by ab initio molecular dynamics (AIMD) simulations, confirmed that Rb2AlAgF6 is structurally, energetically, dynamically, and thermally stable. The electronic band structure reveals a direct band gap of 3.16–3.82 eV (using generalised gradient approximation (GGA) and meta-GGA approximations), indicating its strong suitability for ultraviolet optoelectronic devices. Mechanical analysis indicates ductile, anisotropic behaviour dominated by ionic bonding, which is favourable for device robustness. Optical spectra show intense absorption in the ultraviolet range with low reflectivity and minimal energy loss, highlighting their applicability in UV photodetectors and transparent optoelectronics. Thermoelectric transport calculations revealed a thermoelectric figure of merit (ZT) of 0.65 at 1000 K, demonstrating promising heat-to-energy conversion capabilities at elevated temperatures. These results identify Rb2AlAgF6 as a rare wide-band-gap fluoride double perovskite that simultaneously combines a UV-active optoelectronic response with competitive thermoelectric efficiency. This study establishes a theoretical foundation for the future synthesis and device development of Rb2AlAgF6 and related lead-free multifunctional fluoroperovskites.

ABSTRACT In this study, hybrid density functional theory was employed to investigate Al‐ and P‐related vacancy complexes in a two‐dimensional (2D) SiC monolayer. The structural, electronic, and magnetic properties of , , , , , , , and were examined. The formation energies of these defects were evaluated for first‐nearest‐neighbor ( f ), second‐nearest‐neighbor ( f ), and third‐nearest‐neighbor ( f ) configurations. Under equilibrium conditions, (under Si‐rich conditions) and exhibited the lowest formation energies of 2.10 and 3.04 eV, respectively, in their f configurations. All vacancy complexes showed positive binding energies, indicating thermodynamic stability against dissociation. Al‐related vacancy complexes induced magnetic moments, with exhibiting the highest value of 5.03 , while P‐related complexes produced lower magnetic moments, with reaching 3.10 . The P atom acts as an acceptor only in and as a donor in the remaining P‐related complexes, whereas Al generally donates electrons to neighboring atoms. Moreover, all vacancy complexes exhibited significant spin polarization, highlighting the potential of 2D SiC monolayers for spintronic and electronic device applications.

Rhodium-based double fluoride perovskites offer a chemically stable and environmentally friendly alternative to lead halides; however, many of their compositions remain unexplored. Herein, we report a comprehensive first-principles investigation of previously unstudied Rh-centred double fluoride perovskites Rb2XRhF6 (X = Li, Na, K) to assess their suitability for optoelectronic applications. Structural and thermodynamic analyses confirmed that all compounds satisfied the structural and thermodynamic stability criteria and remained thermally stable up to 1000 K, as verified by ab initio molecular dynamics simulations. Electronic-structure calculations revealed direct band gaps of 1.76-3.52 eV within the GGA-PBE and meta-GGA-TB-mBJ approximations. These wide gaps originate from strong Rh-d/F-p hybridisation, which also produces moderately dispersive band edges favourable for carrier transport. Mechanical analysis indicated ductile behaviour with elastic anisotropy. All compositions exhibited strong absorption in the UV region, together with pronounced plasmonic features near 7 eV, demonstrating their potential for high-energy UV optoelectronic and photonic devices. These results establish design principles linking Rh-d/F-p hybridisation to band-edge dispersion and UV absorption, providing predictive guidance for experimental synthesis and UV-device development.

Ternary Zintl-phase compounds are promising for energy conversion and optoelectronic applications, yet K2P2Pd remains largely unexplored. Here, first-principles density functional theory was employed to investigate the structural, electronic, mechanical, thermodynamic, and thermoelectric properties of orthorhombic K2P2Pd. Stability is confirmed by negative formation energy (−0.54 eV/atom), positive cohesive energy (5.58 eV), phonon spectra without imaginary modes, and molecular dynamics simulations up to 1000 K. K2P2Pd is identified as a direct band gap semiconductor with band gaps of 0.688–1.170 eV. Elastic calculations reveal mechanical stability, ductility, and anisotropy. Thermoelectric analysis shows intrinsic p-type behaviour with a maximum Seebeck coefficient of 230 μV/K and ZT reaching 0.69 at 1000 K due to reduced lattice thermal conductivity. The material also exhibits strong optical absorption (>105 cm−1), highlighting its potential for thermoelectric and photovoltaic applications. These findings provide a rigorous theoretical foundation for subsequent experimental validation and strategic doping protocols.

Antimony arsenide (SbAs), a bulk 3D binary compound has attracted significant interest since its experimental discovery in 2013. This is due to its potential applications in fields such as electronics, topological insulators, optoelectronics, thermoelectrics, and piezoelectrics. In the A7 rhombohedral phase, SbAs manifests a pseudo-layered structure with interlayer interactions mediated by weak van der Waals forces. In the present work, we have employed first-principles calculations to investigate the pressure-dependent structural, stability, and electronic properties of SbAs in the A7 phase. Our results indicate that the lattice parameter along the a-axis shows a continuous reduction under pressure, whereas, the c-axis evolves with anisotropic compression. Bond lengths and bond angles decrease systematically with a linear trend emerging above 60 GPa like the lattice parameters. Symmetry analysis shows a pressure-induced phase transition from the non-centrosymmetric space group R3m to the centrosymmetric R3m. Phonon dispersion relations show a lack of imaginary modes at ambient pressure, but the onset of instability is observed between 20 and 40 GPa, with the appearance of imaginary modes that decrease in intensity from the former to the latter stated pressure point. However, these modes dissipate from around 60 GPa and above signifying the material's dynamic stability at high pressures. On the electronic front, SbAs exhibits a transition from a semimetallic to a metallic state with increasing pressure accompanied by a rise in the Fermi energy. Furthermore, spin-orbit coupling (SOC) has also been observed to play a significant role in the material's electronic characteristics.

This study investigated the structural, electronic, elastic, mechanical, thermodynamic, optical, and thermoelectric properties of the Rb2NaIrF6lead-free double perovskite compound using first-principles methods. The structural stability of the perovskite was confirmed by the Goldschmidt tolerance and octahedral factors. Dynamic stability was confirmed through the negative energy of formation and positive frequency modes of the phonon dispersion curve. The dynamic stability results suggest that the studied compound could be potentially synthesised experimentally. The Rb2NaIrF6 compound is a direct semiconductor with electronic band gaps within the range of 2.14–3.76 eV, computed using different approximations. The mechanical stability was confirmed by the elastic calculation results. The Rb2NaIrF6compound was found to be ductile, ionic, and anisotropic. The optical properties showed that Rb2NaIrF6 strongly absorbs light in the ultraviolet region, which is desirable for ultraviolet-photosensitive materials in optoelectronic devices. The computed thermoelectric figure of merit of the Rb2NaIrF6compound is 0.81 at 1000 K, suggesting high thermoelectric efficiency. These findings demonstrate the potential of Rb2NaIrF6 lead-free double perovskite compound for optoelectronic and thermoelectric applications. Therefore, our investigation offers theoretical insights that can lead to the experimental synthesis and study of Rb2NaIrF6lead-free double perovskites.

The possibility of using graphane monolayer crystals as an electrode material is becoming popular. Graphane is stable at room temperature and has a large surface area, but its chemical inertness hinders its direct interactions with Li ions. In this study, we performed density functional theory calculations to study the energetic stability and structural and electronic properties of Li on graphane with various CH divacancy configurations (v12, v13, and v14). The results show that the adsorption of the Li atom reduces the formation energy of the CH divacancy configurations. The Li-v12 is most stable with the highest binding energy of 3.25 eV/Li and relaxes to in-plane with other C atoms. Altering the Li charge state to have Li−1-v12 or Li+1-v12 affects the energetic stability and electronic characters of Li-v12. The Li−1-v12 (Li+1-v12) slightly (greatly) reduces the binding force between the Li and v12 configuration, and furthermore it improves (deteriorates) the conductivity of the structure. Further investigation of graphane with vacancies is encouraged due to these intriguing observations, as it holds promise for potential utilization as an electrode material.

Defect complexes have a significant impact on the structural, electronic, optical and electrical properties of semiconductors. Several defect complexes formed by n -type and p -type atoms in Ge have been implemented for the development of improved modern microelectronic devices. However, there is no reported study on the substitutional-interstitial defect complexes formed by trivalent atoms in Ge. This paper presents a hybrid density functional theory study of the structural, electronic, formation and defect levels induced by the trivalent substitutional-interstitial (B _Ge B _i , Al _Ge Al _i , Ga _Ge Ga _i and In _Ge In _i ) defect complexes in Ge. The formation energy results showed that the trivalent substitutional-interstitial defect complexes in Ge were formed with relatively low energy. Ga _Ge Ga _i under equilibrium conditions is the most energetically favourable, with a formation energy of 3.95 eV. All trivalent atoms are bound with their respective substitutional and interstitial atoms without dissociation. With respect to their ability to form as a defect cluster, the In _Ge In _i is the most stable defect complex, with a binding energy of 2.91 eV. Except for the Ga _Ge Ga _i , all studied defect complexes are electrically active. The B _Ge B _i and Al _Ge Al _i induced a single acceptor level, while the In _Ge In _i induced active donor levels. The acceptor defect level induced by the B _Ge B _i is deep, and that of the Al _Ge Al _i is shallow, close to the conduction band. The results of this study are important, as they provide theoretical insights into the experimental characterization of the substitutional-interstitial defect complexes formed by trivalent impurities in germanium, which could help to improve Ge-based microelectronic devices.

First-principles calculations based on density functional theory (DFT) were carried out to study the energetic stability and electronic properties of a bimetallic-doped α-Fe2O3 photoanode surface with (Zn, Ti) and (Zn, Zr) pairs for enhanced PEC water splitting. The doped systems showed negative formation energies under both O-rich and Fe-rich conditions which make them thermodynamically stable and possible to be synthesised. It is found that in a bimetallic (Zn, Ti)-doped system, at a doping concentration of 4.20% of Ti, the bandgap decreases from 2.1 eV to 1.80 eV without the formation of impurity states in the bandgap. This is favourable for increased photon absorption and efficient movement of charges from the valance band maximum (VBM) to the conduction band minimum (CBM). In addition, the CBM becomes wavy and delocalised, suggesting a decrease in the charge carrier mass, enabling electron–holes to successfully diffuse to the surface, where they are needed for water oxidation. Interestingly, with single doping of Zr at the third layer (L3) of Fe atoms of the {0001} α-Fe2O3 surface, impurity levels do not appear in the bandgap, at both concentrations of 2.10% and 4.20%. Furthermore, at 2.10% doping concentration of α-Fe2O3 with Zr, CBM becomes delocalised, suggesting improved carrier mobility, while the bandgap is altered from 2.1 eV to 1.73 eV, allowing more light absorption in the visible region. Moreover, the photocatalytic activities of Zr-doped hematite could be improved further by codoping it with Zn because Zr is capable of increasing the conductivity of hematite by the substitution of Fe3+ with Zr4+, while Zn can foster the surface reaction and reduce quick recombination of the electron–hole pairs.

First-principles calculations of Zinc (Zn) doped {0001} and {01 (1) over bar2} hematite surfaces for improved photoelectrochemical water splitting have been studied. The single Zn-doped systems were found to be energetically favourable (negative formation energies) and the stability increased with increasing concentration of Zn atoms. Our results show that even with mono-doping of Zn on the topmost layer L1 structure of the {0001} alpha-Fe2O3 surface, the band gap can be decreased without impurity states in the band structure which normally acts as recombination centres. At the doping concentration of 4.20% of Zn atoms on L1 of {0001} surface, the conduction band minimum (CBM) is shifted upwards by 0.23 eV as compared to the bulk. In addition to the decrease in the band gap, the CBM of the single doped layer 2 (DL21) and layer 3 (DL31) of the {01 (1) over bar2} surface become wavier and delocalised suggesting improved electron mobility of hematite surface. Charge density difference plots and Bader charge analysis showed the accumulation of charge at the top of the surface with more pronounced charge depleting from Zn atom and accumulating on O and Fe neighbouring atoms, implying that the photo generated charge carriers can efficiently diffuse to the surface for enhanced interfacial charge transfer to the adsorbates. The electronic properties exhibited by doping of Zn on the two hematite surfaces postulate that surface doping is likely to strengthen the electrocatalytic activity of hematite for water splitting.

Density Functional Theory (DFT) calculations study of Cu doped {0001} and {01–12} surfaces of hematite for enhanced water splitting have been carried out. The doping was restricted to planes in the vicinity of the surface, specifically from the top most layers to the third inner layer of Fe atoms. Thermodynamic stabilities were evaluated based on surface energies and formation energies. The evaluation of thermodynamic stabilities (negative formation energy values) shows that the systems are thermodynamically stable which suggest that they can be synthesized in the laboratory under favorable conditions. Doping on the top most layer yields the energetically most favorable structure. The calculated charge density difference plots showed the concentration of charge mainly at the top of the surface (termination region), and this charge depleted from the Cu atom to the surrounding Fe and O atoms. This phenomenon (concentration of charge at the top of the surface) is likely to reduce the distance moved by the charge carriers, decrease in charge recombination leading to facile transfer of charge to the adsorbate and, suggesting improved photoelectrochemical water oxidation activity of hematite. The analysis of electron electronic structure reveals that Cu doped surface systems does not only decrease the band gap but also leads to the correct conduction band alignment for direct water splitting without external bias voltage.

Ab-initio calculations within the framework of density functional (DFT) have been performed to study the electronic and optical properties of Be and N co-doped graphene. The results have been compared with that of Be-doped, N-doped, and pristine graphene. The effect of doping and isomerization on the electronic and the optical properties of these systems have been studied by varying the impurity concentrations of Be-doped and N-doped graphene systems from 3.13% through 12.5%, whereas for Be and N co-doped graphene, the concentration has been varied from 6.25% through 25.0 % impurity concentration. The formation energies of the systems with different impurity configurations were calculated to examine their relative stabilities. It was found that for Be-N co-doped graphene, the configuration of which N and Be coexisting as the nearest neighbors is energetically the most favorable configuration. Moreover, at the same impurities concentration, Be-N co-doped graphene was observed to be more stable than Be-doped graphene due to its lower formation energy. Thus these results reveal that it is much easier to synthesize Be-N co-doped graphene than to synthesize Be-doped graphene. Hence, the relatively high formation energy of Be-doped graphene could be the reason why the system is yet to be synthesis experimentally despite a recent theoretical report on it. The results of the electronic structure calculations reveal that Be-N co-doped and Be-doped graphene are p-type semiconductors while N-doped graphene has been verified to be an n-type semiconductor. For all the doped systems considered in this study, it was observed that the size of the band gap increases with impurity concentration with respect to the aforementioned energetically most favorable isomer. At impurity concentration of 3.13%, a minimum band gap of 0.44 eV and 0.21eV was realized for Be-doped and N-doped graphene respectively while at 12.5 % corresponding maximum gap of 1.41 eV and 0.6 eV were observed. Besides, Be-N co-doped graphene was found to have a minimum band gap of 0.43 eV at 6.25% and a maximum gap of 1.54 eV at 25.0% impurities concentration. The dielectric matrices of the doped systems were calculated using first-order time-dependent perturbation theory in the simple dipole approximation. It was found that all the systems investigated were transparent within the frequency interval of 7.0eV-10eV for parallel EM polarization. In general, we observed that the optical properties of the doped systems investigated respond to doping concentration differently across the EM spectrum with respect to the anisotropic signature of the host system. The results of our study demonstrate that the band gap of graphene can be tailored to meet the requirements of specific applications in nanoelectronic and optoelectronic devices.

The application of germanium (Ge) as a promising material for complementary metal-oxide semiconductors (CMOS) technology is attracting attention due to its narrow band gap, high carrier mobility and low voltage operations. Recent experimental and theoretical studies revealed that dopants in Ge cluster with vacancies forms with lower energies and contribute to low activation of dopants impurity in Ge. DFT electronic simulation have been used to provide concise information about the formation of defect clusters and complexes that influence diffusion mechanisms in Ge. Our main objective in this study is to use simulations based on ͑DFT to calculate the structural, electronic properties and interactions between acceptors and Ge in different configurations with a view to finding the most energetically stable configuration of various defect complexes in Ge. By means of density functional theory (DFT), we present ab-initio calculation of interactions between A (A: Be,Mg, Ca, Sr, Ba, Ga, In) vacancy complexes (A-VGe) and vacancy-interstitial complexes (A-VGeIA) in two configurations of the hexagonal (H) and tetrahedral (T) in Ge. These calculations employed a projector augmented wave (PAW) pseudopotentials within the generalized gradient approximation (GGA). The geometric structures and formation energies of A-VGe and A-VGeIA in both the T and H configurations for the neutral charge state were obtained. The formation energies of A-VGe were low and energectically favourable with Ga-VGe and Ca-VGe forming with the lowest formation energies at -1.24 and -0.38 eV respectively. For the A-VGeIA, the results of the H configuration were more energetically favourable and forms with lower formation energies than the T configuration. The Ca-VGeICa and Be-VGeIBe forms with the lowest formation energies of -2.59 and -1.49 eV respectively. The stability of the A-VGeIA and A-VGe complexes in Ge were obtained from their binding energies. The binding energies (Eb ) which are defined as the energy required to split up the defects cluster into well separated non-interacting defect is given as Eb = E(formation)(VGe) + E(formation)(AGe) - E(formation){defect-complex}, where E(formation)(VGe), E(formation)(AGe) and E(formation)(defect-complex) are the formation energies of the neutral charge state of the germanium vacancy, interstitials and defect-complexes. The above equation could be interpreted as the energy gain of the bonded structure with respect to the isolated components. Positive binding energies suggest that the defect complexes are stable and cannot easily dissociate. The calculated binding energies of both the A-VGe and the A-VGeIA displayed the ability of these complexes to form without dissociation. For the A-VGeIA, the H configuration forms with more favourable binding energies than the T configuration. In summary the detailed calculated results we have presented are expect to be useful in the process modeling of Ge-based devices.