Narrow Results

The advancement of science and technology is essential for the progress of nanotechnology, which plays a pivotal role in the development of miniaturized and energy-efficient devices. This investigation delves into the As-doped structures within one-dimensional germanene nanoribbons. Utilizing Density Functional Theory (DFT) in conjunction with the Vienna Ab initio Simulation Package (VASP), the study explores the electro-optical properties of the material influenced by As doping, examining both the doping position and density’s effects. Results indicate As significantly alters the electro-optical characteristics, with the semiconductor structure transitioning to metals in top and valley configurations, while meta and para configurations retain semiconductor properties with an indirect band gap. Analysis of bond length, bond angle, magnetism, formation energy and charge density difference elucidates As’ impact on hexagonal structure stability and electromagnetism properties of the system. Furthermore, a comprehensive investigation of optical properties not only offers insights into material systems but also highlights potential applications in optical communications and sensing technologies.

In this paper, we investigated the structural, elastic, topological-electronic properties as well as optical properties of two half-Heusler (HH) heavy fermions-based compounds: HoPtBi and HoPdBi. We accomplished our calculations in the framework of density functional theory (DFT), based on the full potential linearized augmented plane wave (FP-LAPW). Both compounds are antiferromagnetic (AFM) type-II as reported by experimental data so we carried out our study in the AFM type-II configuration. Considering the spin-orbit coupling, we found that the hydrostatic pressure leads to a phase transition from the trivial semimetal to the topological semimetal (TSM) because of band inversion for HoPdBi with no apparent effect of hydrostatic pressure on the topological phase for HoPtBi. We also studied their optical properties, without and with hydrostatic pressure. The first peak in reflectivity, absorption, optical conductivity spectra and energy loss factor are strongly influenced by the hydrostatic pressure. Both compounds exhibit a considerable first absorption peak in the visible and ultraviolet ranges and they are best candidates for solar cells considered essential in renewable energy.

The potential applications of the cubic phase of CsNbO₃ perovskite have been explored by examining its elastic, electronic, and photocatalytic characteristics using a first-principles approach. The structural robustness when subjected to pressure has been verified by studying the computed elastic constants. Its substantial elastic moduli, hardness, and toughness values propose its suitability for various engineering applications. A transition from flexibility to fragility is observed at pressures exceeding 10GPa. The CsNbO₃ material demonstrates an indirect and narrow band gap, making it a promising candidate in optoelectronic applications. Changes in the band gap due to pressure indicate adjustments in orbital hybridization. The material’s low effective carrier mass and high carrier mobility anticipate favorable electrical conductivity. Assessments of the potentials at the conduction band (CB) and valence band (VB) edges underscore the remarkable capacity of CsNbO₃ for activities such as water-splitting and promoting sustainable energy production.

The electronic and magnetic properties of Be${}_{1-x}$(Gd,Eu,Tb)${}_x$O (with $x$ values of 0.125, 0.25, and 0.375) were systematically investigated using the full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). Exchange and correlation potentials were computed employing the generalized gradient approximation (GGA) and GGA plus-modified Becke–Johnson potential (TB-mBJ) approximations. Our findings demonstrate that the incorporation of X into BeO induces magnetism in the compound. Specifically, BeO doped with Gd, Eu, and Tb at $x=0.125,0.25$, and 0.375 exhibits half-metallic behavior, characterized by integer magnetic moments. These results indicate the potential of these compounds to serve as novel half-metallic materials for future spintronics applications, offering exciting prospects in the field.

BaHfS₃ and BaZrS₃, two chalcogenide perovskites, show significant promise for next-generation optoelectronic devices due to their adjustable bandgaps, excellent carrier mobilities, and versatile properties. Using density functional theory (DFT) via the WIEN2k package, this study reveals their bandgap energies of 2.05eV and 1.63eV, respectively, situating them in the visible range and making them suitable for photovoltaic (PV) applications. Additionally, both materials satisfy thermodynamic criteria for hydrogen production through water splitting, confirming their photocatalytic potential. Their thermoelectric performance, measured by the figure of merit (ZT) also indicates moderate potential at elevated temperatures. Strain engineering further enhances the PV performance, where a biaxial compressive strain of −6% boosts power conversion efficiencies (PCEs) by 8.34% for BaHfS₃ and 3.30% for BaZrS₃. For photocatalysis, uniaxial and biaxial strains optimize optical absorption and water-splitting kinetics. Furthermore, the thermoelectric properties slightly improve under strain effect. These findings highlight the multifunctional potential of BaHfS₃ and BaZrS₃ for PV, photocatalytic, and thermoelectric applications, with strain engineering providing a robust strategy for performance optimization.

Favored structures of SiO_n monolayers on Mo(112) surface have been studied using the total energy minimization technique based on DFT semirelativistic approach. In the [SiO₄] complexes, which form the c(2 × 2) silica structure on the Mo(112), the bonding of the Si atoms with the surface is accomplished through the oxygen atoms. The structure with a symmetric position of oxygen atoms has been found to be the most favorable. In this structure, two oxygen atoms occupy bridge-on-row sites on the Mo(112) surface, with Si atoms between them, while oxygen atoms in the troughs appear not in expected threefold sites, but adjust their positions along the middle lines of the troughs. Estimated main phonon frequency and density of states for the symmetric [SiO₄] structure agree well with experimental results.

We have performed Density Functional Theory calculations in the Generalized Gradients Approximation for the (001) surface of the intermetallic compound TiFe. We have focused on the interplay between spin polarization and surface relaxations, and the influence of the chemical species at the surface. We found that the surface shows a magnetic ordering. The magnetic moment at the surface layer depends strongly on the surface termination, being much larger for the case of Fe than Ti termination (3.11 and 0.29 μ_B/atom, respectively). The magnetic moments show an alternating behavior with a slow decaying as we go inside the material. On the other hand, the modification of the atomic positions due to the surface relaxation results in a very small influence on the magnetic moment with respect to the ideal, nonrelaxed configuration.

A systematic study of unrelaxed and relaxed surface characters on the TiO₂ (101) surface has been carried out by first-principles calculations using plane-wave pseudopotential method. We find that O_2c atoms have an inward relaxation of 0.012 Å and Ti_5c atoms have an outward relaxation of 0.155 Å by taking a 24-layer slab with 5 Å vacuum width to consider the atomic relaxations, in good agreement with other theoretical values. The slab thickness has significant effect on the quality of band structure and density of states, and 24-layer slab is sufficient to present the electronic properties of TiO₂ (101) surface. Atomic relaxations result in a large transfer of surface charges from outermost layer to inner layer, and the surface bonds have a rehybridization, which makes the ionization reduce and the covalence increase; we believe that it causes the surface bond shorten. A fine analysis of band structure and density of states of the TiO₂ (101) surface shows that the surface relaxation induces the transformation from semi-metallic to semiconducting characteristic.

In calculating band structure, the local density approximation and density functional theory are widely popular and do reproduce a lot of the basic physics. Regrettably, without some fine tuning, the local density approximation and density functional theory do not generally get the details of the experimental band structure correct, in particular the band gap in semiconductors and insulators is generally found to be too small when compared with experiment. For experimentalists using commercial packages to calculate the electronic structure of materials, some caution is indicated, as some long-standing problems exist with the local density approximation and density functional theory.

The binding energies and related energies of associative desorption for oxygen on close-packed (W(110), Mo(110), and Ru(0001)) and furrowed (W(112), Mo(112), and ) surfaces have been calculated by DFT method with generalized gradient approximation for exchange-correlation potential in the revised-Perdew–Burke–Ernzerhof form. The unified approach allows one for a direct comparison of calculated binding energies for different transition metals and different surface geometries, thus revealing the trends that are essential for catalytic properties of surfaces with adsorbed oxygen layers.

The co-adsorption of carbon monoxide and benzene on Co(0001) has been studied using density functional calculations. We used the ordered surface unit cell. A comparison of the co-adsorption with CO and benzene two-dimensional networks is also given. The electronic structure reveals that the CO orbitals interact with benzene and Co layer. Regarding the bonding, the Co–Co overlap population decrease 18% after benzene adsorption and increase a little after CO adsorption with a net 14.6% decrease in the co-adsorption system. The CO–benzene interaction is shown by the changes in the C–O (CO) and C–H (benzene) bonds.

In this work, the p-type doping of the S_A type stepped Ge(100) surface by a diborane (B₂H₆) gas flow has been simulated by the possible dissociation and adsorption models. The most probable dissociation model of B₂H₆ and adsorption models of the fragments of B₂H₆ on the stepped Ge(100) surface have been determined by the local minimum total energy and/or binding energy calculations based on the Density functional (B3LYP/6-3g) and Hartree–Fock (HF/STO-3g) theories, respectively. The present calculations have shown that, the step region (for both up and down terraces) of the stepped Ge(100) surface has the most attractive sites for BH₃ molecules determined to be the first dissociation fragments of B₂H₆ by an external energy of ~ 1.3 eV. It has been found that, at the first step of the adsorption, BH₃ can dissociate to BH₂ and BH fragments on the stepped Ge(100) surface. While BH₃ and BH₂ products prefer to be attached to a single surface Ge atom, BH is bridged between two adjacent surface Ge atoms. According to the present optimization calculations, the p-type doping process of the stepped Ge(100) surface has started with the adsorption of BH₃ on the electron deficient site (buckled down) of the Ge dimer bond close to the step edge and ended with the substitutional occupation of the Ge site in the layers of the surface by B atom. The beginning of the p-type doping of the stepped Ge(100) surface has been illustrated by the electronic states of B appeared in the optical energy gap of Ge very close to the edge of the HOMO.

The interaction between the H₂ molecule and the PdAg, PdAu, PtAg and PtAu bimetallic dimers deposited on the MgO(100) surface is investigated using density functional theory (DFT). The bimetallic dimers, whose molecular axes are considered to be perpendicular to the support surface, are adsorbed on top of an oxygen atom. Within this adsorption mode, the dimers prefer the orientation in which their Pd or Pt end is closer to the oxygen atom. The Ag and Au ends of the MgO-supported dimers capture the H₂ molecule with small exoenergetic effects. The spontaneous dissociation of H₂ on these ends does not occur. Thus, the MgO support decreases the ability of the dimers to adsorb and dissociate the H₂ molecule. From a catalytic viewpoint, it means that the activity of small bimetallic clusters toward the dissociative adsorption of H₂ is reduced when they are arranged on MgO. On the other hand, the results of our calculations show that the presence of the MgO support strengthens the binding of H atoms inside the PdAu, PtAg and PtAu dimers.

The structural and electronic properties of BN_xAs_1-x alloys have been investigated in the total range of nitrogen by the FP-LAPW method based on DFT within the EV-PW-GGA scheme. The equilibrium lattice constants, bulk moduli, first-order pressure derivatives of the bulk moduli, and cohesive energies have been obtained by total energy calculations of the alloys after both volume and geometry optimizations. The large bowing parameters found for the lattice constants and bulk moduli have demonstrated that the validity of Vegard's linear rule in the definitions of these structural features of the BN_xAs_1-x alloys is broken. The energy bands and the effective masses of the alloys have been calculated as a function of nitrogen concentration. The large bowing displayed by the variation of the energy gaps has indicated the band gap engineering capacity of the BN_xAs_1-x alloys and again in deviations from Vegard's linear rule. The effective electron masses calculated either at the edges of the conduction bands or along the directions approaching the edges of the conduction bands are all found to be small with respect to the effective electron masses in the BAs and BN compounds calculated at the Δ_min and X points, respectively.

This study presents an ab initio investigation of the interaction of Al₅H₁₂ with the alloying transition elements (TM) in the TMAl₅H₁₂ (TM = Ti, V, Fe, Co and Ni). Hydrogen atoms are found to prefer the tetrahedral sites in the fcc Al bulk system with a binding energy that is more energetically favored than octahedral sites by 0.17 eV. Absorbed H atoms in Al increase the lattice constant and decrease the cohesive energy by 13.8% and 32.7%, respectively. The present values of the H–H bond length (0.75 Å) and the dissociation energy of H₂ (4.47 eV) are in good agreement with the previously measured values. The binding energy of H atoms in TiAl₅H₁₂ system is higher than the other studied systems due to the hybridization between s-state of H and d-state of Ti atom. The magnetic moments of Fe in FeAl₅H₁₂ system and Ni in NiAl₅H₁₂ system are enhanced as compared to the dehydrogenated system.

Molecular hydrogen adsorption on MOF-210 was evaluated at the density functional theory level. The most stable H₂ adsorption occurs near the acetenyls in the organic linker, but its binding energy (0.113 eV) is not sufficient to satisfy the minimum value (0.24 eV) required for practical applications. Meanwhile, Li cation-decorated MOF-210 has the average hydrogen adsorption energies of 0.28 eV, and its saturated hydrogen storage capacity reaches 5.35 wt.%.

Effect of light alkali metal (Li and Na) decorated on the C₅₉B heterofullerene for hydrogen storage is considered using DFT-MPW1PW91 method. Results show that Li and Na atoms strongly prefer to adsorb on top of five-member and six-member ring where a carbon atom is replaced by a boron atom. Significant charge transfer from the alkali metal to the C₅₉B compensates for the electron deficiency of C₅₉B and makes the latter aromatic in nature. Corrected binding energies of hydrogen molecule on the alkali-doped C₅₉B using counterpoise method, structural properties and NBO analysis indicate that first hydrogen molecule is adsorbed physically and does not support minimal conditions of DOE requirement. Finally, positive values of binding energies for the adsorption of a second hydrogen molecule show that alkali doped C₅₉B are capable of storing a maximum of one hydrogen molecule.

Interaction of CO and NO molecules by different orientations on (BN)_n=3-5 clusters have been studied at the B3LYP/6-311+G* level of theory. Total electronic energies have been corrected for geometrical counterpoise (gCP) and dispersion (D3) energies at the B3LYP/6-31G* level. Formation of a new sigma bond between the gas and (BN)₃ cluster, atom in molecules (AIM) results, density of states spectrums (DOS), molecular electrostatic potential (MEP) surfaces, and visualization of wave function of molecular orbitals in the nearest bonding regions to the Fermi level have confirmed that adsorption of CO by carbon end atom, and NO by nitrogen end atom is covalent in nature, so that the charge transfer is occurred from gas molecule to the cluster.

The electronic band structure, density of states (DOS) and interlayer interaction in Li-intercalated graphene bilayers are studied by means of density functional theory (DFT) calculations. It has been found that for a pristine bilayer, the relative shift of graphene layers from AB stacking configuration, pertinent to a bulk graphite, to AA configuration results in the opening of the bandgap at Fermi level, so that the bilayer becomes a semiconductor. The Li intercalation of the graphene bilayer significantly increases the density of states at Fermi level, which can be considered as an increased metallicity. The electronic density in the space between graphene layers also substantially increases and leads to related increase of the interlayer interaction. We hope that the obtained results of calculations will be useful for various applications of Li-intercalated graphene layers in nanoelectronics.

In the present work, we apply wurtzoids nanocrystals with density functional theory to explain the sensitivity of ZnO nanostructures towards hydrogen and oxygen molecules. Present results of ZnO nanocrystals’ sensing to H₂ and O₂ molecules show a reduction in the energy gap and hence electrical resistivity of ZnO nanocrystals upon attachments of these molecules in agreement with experiment. The results also show that higher temperatures increase the sensitivity of ZnO wurtzoids towards H₂ and O₂ molecules with the maximum sensitivity approximately at 390${}^{\circ }$C and 417${}^{\circ }$C for H₂ and O₂ molecules, respectively, after which it begins to decline according to calculated Gibbs free energy. These temperatures are comparable with experimentally reported operating temperatures of 325${}^{\circ }$C and 350${}^{\circ }$C for the two gases, respectively. The main reaction mechanism is the dissociation of H₂ or O₂ molecules on ZnO nanocrystal surface in which hydrogen and oxygen atoms are attached to neighboring Zn and O surface atoms. The removal of these molecules from the surface is also performed by the formation of H₂ and O₂ molecules prior to their removal from the ZnO nanocrystal surface. Electronic charge transfers to the adsorbed atoms and molecules confirm and illustrate the mechanism mentioned above.