Optical excitations of graphene-like materials: group III-nitrides.

By using first-principles calculations, we have studied the electronic and optical characteristics of group III-nitrides, such as BN, AlN, GaN, and InN monolayers. The optimized geometry, quasi-particle energy spectra, charge density distributions, band-decomposed charge densities, and Van Hove singularities in density of states are described in the work using physical and chemical pictures and orbital hybridizations found in B-N, Al-N, Ga-N, and In-N chemical bonds. Moreover, the dielectric functions, energy loss functions, absorption coefficients, and reflectance spectra with electron-hole interactions of optical properties are successfully achieved.

Correction: Theoretical investigations of the electronic and optical properties of a GaGeTe monolayer.

[This corrects the article DOI: 10.1039/D3RA03160H.].

Theoretical investigations of the electronic and optical properties of a GaGeTe monolayer.

Our study focused on exploring the electronic and optical characteristics of the GaGeTe monolayer using first-principles calculations. Our findings showed that this material has remarkable physical and chemical properties attributed to its unique band structure, van Hove singularities in the density of states (DOS), charge density distributions, and charge density differences. We also observed excitonic effects, multiple optical excitation peaks, and strong plasmon modes in the energy loss functions, absorption coefficients, and reflectance spectra, which contribute to its enriched optical response.

Fundamental features of AlCl -/AlCl-graphite intercalation compounds of aluminum-ion-based battery cathodes.

Up to now, many guest atoms/molecules/ions have been successfully synthesized into graphite to form various compounds. For example, alkali-atom graphite intercalation compounds are verified to reveal stage-n structures, including LiC and LiM [M = K, Rb, and Cs; = 1, 2, 3; 4]. On the other side, AlCl -ion/AlCl-molecule compounds are found to show stage-4 and stage-3 structures at room and lower temperatures, respectively.

Electronic and optical properties of graphene, silicene, germanene, and their semi-hydrogenated systems.

We investigate the geometric, electric, and optical properties of two-dimensional honeycomb lattices using first-principles simulations. The main focus of this work is on the similarities and differences in their characteristics, as well as the delicate connection of orbital hybridizations and spin-polarizations with electronic and optical properties. Graphene, silicene, germanene, and their semi-hydrogenated systems, in turn, display sp, sp-sp, and sps hybridizations.

First-principles simulation insights of electronic and optical properties: LiPSCl system.

We perform the electronic and optical properties of the LiPSCl compound using first-principles calculation. The featured physical and chemical pictures and orbital hybridizations in all Li-S and P-S chemical bonds are clearly exhibited, such as the optimized geometry, the quasi-particle energy spectra, the band-decomposed charge densities, and the van Hove singularities in the density of states. Furthermore, the calculated results of the presence and absence of electron-hole interactions in optical responses are achieved successfully through the dielectric function, the energy loss functions, the absorption coefficients, and the reflectance spectra.

Fundamental Properties of Hydrogen-Functionalized GaSe Monolayer.

Functionalization reveals potential opportunities for modifying essential properties and designing materials due to the strong interaction between functionalized atoms and the surface. Among them, hydrogenation possesses such a way to control electronic and optical characteristics. In this paper, the stability and transformed electronic, optical properties of H-functionalized GaSe in two cases (single and double sites) were reported that exhibit the effects of hydrogen functionalization via first-principles calculations.

Electronic and Optical Properties of CsGeX (X= Cl, Br, and I) Compounds.

We used first-principles calculations to investigate the electrical and optical properties of CsGeX (X = Cl, Br, and I) compounds. These materials present rich and unique physical and chemical phenomena, such as the optimal geometric structure, the electronic band structure, the charge density distribution, and the special van Hove singularities in the electronic density of states. The optical properties cover a slight red shift of the optical gap, corresponding to weak electron-hole interactions, strong absorption coefficients, and weak reflectance spectra.

Essential Electronic Properties of Silicon Nanotubes.

In this work, the various electronic properties of silicon nanotubes (SiNTs) were investigated by the density functional theory. The cooperative and competitive relationships between the chiral angle, periodic boundary conditions, and multi-orbital hybridizations create unusual narrow gaps and quasi-flat bands in the ultra-small armchair and zigzag tubes, respectively. The features varied dramatically with tube radii.

Spin-dependent Optical Excitations in LiFeO.

The three-dimensional ternary LiFeO compound presents various unusual properties. The main features are thoroughly explored by using many-body perturbation theory. The concise physical/chemical picture, the critical spin polarizations, and orbital hybridizations in the Li-O and Fe-O bonds are clearly examined through geometric optimization, quasi-particle energy spectra, spin-polarized density of states, spatial charge densities, spin-density distributions, and strong optical responses.

Oxidation and Degradation of WS Monolayers Grown by NaCl-Assisted Chemical Vapor Deposition: Mechanism and Prevention.

The preservation of two-dimensional WS in the environment is a concern for researchers. In addition to water vapor and oxygen, the latest research points out that degradation is directly related to light absorption. Based on the selection rules of nonlinear optics, two-photon absorption is dipole forbidden in the exciton 1s states, but second-harmonic generation (SHG) is allowed with virtual transitions.

Optical absorption spectra of Xene and Xane (Xsilic, german, stan).

We study optical absorption spectra of Xene and Xane (X = silic, german, stan). The results show that the optical absorption spectra of Xenes are dominated by a sharp peak near the origin due to direct interband transitions near thepoint of the Brillouin zone. Meanwhile, the optical absorption spectra of Xanes are characterized by an excitonic peak.

Feature-Rich Geometric and Electronic Properties of Carbon Nanoscrolls.

How to form carbon nanoscrolls with non-uniform curvatures is worthy of a detailed investigation. The first-principles method is suitable for studying the combined effects due to the finite-size confinement, the edge-dependent interactions, the interlayer atomic interactions, the mechanical strains, and the magnetic configurations. The complex mechanisms can induce unusual essential properties, e.

Excitonic effects in the optical spectra of LiSiO compound.

LiSiO compound exhibits unique electronic and optical properties. The state-of-the-art analyses, which based on first-principle calculations, have successfully confirmed the concise physical/chemical picture and the orbital bonding in Li-O and Si-O bonds. Especially, the unusual optical response behavior includes a large red shift of the onset frequency due to the extremely strong excitonic effect, the polarization of optical properties along three-directions, various optical excitations structures and the most prominent plasmon mode in terms of the dielectric functions, energy loss functions, absorption coefficients and reflectance spectra.

Diversified Phenomena in Metal- and Transition-Metal-Adsorbed Graphene Nanoribbons.

Adatom-adsorbed graphene nanoribbons (GNRs) have gained much attention owing to the tunable electronic and magnetic properties. The metal (Bi, Al)/transition metal (Ti, Fe, Co, Ni) atoms could provide various outermost orbitals for the multi-orbital hybridizations with the out-of-plane π bondings on the carbon honeycomb lattice, which dominate the fundamental properties of chemisorption systems. In this study, the significant similarities and differences among Bi-/Al-/Ti-/Fe-/Co-/Ni-adsorbed GNRs are thoroughly investigated by using the first-principles calculations.

Orbital-hybridization-created optical excitations in LiGeO.

The three-dimensional ternary LiGeO compound presents various unusual essential properties. The main features are thoroughly explored from the first-principles calculations. The concise pictures, the critical orbital hybridizations in Li-O and Ge-O bonds, are clearly examined through the optimal geometric structure, the atom-dominated electronic energy spectrum, the spatial charge densities, the atom and orbital-decomposed van Hove singularities, and the strong optical responses.

Rich -type-doping phenomena in boron-substituted silicene systems.

The essential properties of monolayer silicene greatly enriched by boron substitutions are thoroughly explored through first-principles calculations. Delicate analyses are conducted on the highly non-uniform Moire superlattices, atom-dominated band structures, charge density distributions and atom- and orbital-decomposed van Hove singularities. The hybridized 2 -3 and [2s, 2 , 2 ]-[3s, 3 , 3 ] bondings, with orthogonal relations, are obtained from the developed theoretical framework.

Unusual features of nitrogen substitutions in silicene.

The quasiparticle properties resulting from charge and spin are clearly identified in nitrogen-substituted silicenes, for which a theoretical framework is successfully developed from first-principles calculations. Such systems create extremely non-uniform chemical and physical environments through the distribution of the guest atoms. They present unusual geometric, electronic, and magnetic properties, which can be identified from the optimal honeycomb lattices, the atom- and spin-dominated energy spectra, the spatial charge density distributions, and the atom-, orbital- and spin-projected van Hove singularities [the net magnetic moments].

Unusual electronic excitations in ABA trilayer graphene.

The tight-binding model is closely associated with the modified random-phase approximation to thoroughly explore the electron-electron interactions in trilayer AB-stacked graphene. The intralayer and interlayer atomic/Coulomb interactions dominate the collective and electron-hole excitations. The unusual energy bands are directly reflected in the diverse transferred momentum-frequency phase diagrams.

Essential geometric and electronic properties in stage- graphite alkali-metal-intercalation compounds.

The rich and unique properties of the stage- graphite alkali-metal-intercalation compounds are fully investigated by first-principles calculations. According to the main features, the lithium and non-lithium (Na, K, Rb, Cs) systems are quite different from each other in stacking configurations, intercalant alkali-metal-atom concentrations, free conduction electron densities, atom-dominated and (carbon, alkali metal)-co-dominated energy bands, and interlayer charge density distributions. The close relations between the alkali-metal-doped metallic behaviors and the geometric symmetries are clarified through the interlayer atomic interactions.

First-principles studies of electronic properties in lithium metasilicate (LiSiO).

Lithium metasilicate (LiSiO), which could serve as the electrolyte material in Li-based batteries, exhibits unique lattice symmetry (an orthorhombic crystal), valence and conduction bands, charge density distribution, and van Hove singularities. Delicate analyses, based on reliable first-principles calculations, are utilized to identify the critical multi-orbital hybridizations in Li-O and Si-O bonds, 2s-(2s, 2p , 2p , 2p ) and (3s, 3p , 3p , 3p )-(2s, 2p , 2p , 2p ), respectively. This system shows a huge indirect gap of 5.

Fundamental Properties of Metal-Adsorbed Silicene: A DFT Study.

Sodium, magnesium, and aluminum adatoms, which possess one, two, and three valence electrons, respectively, in terms of 3s, 3s, and (3s, 3p) orbitals, are very suitable for helping us understand adsorption-induced diverse phenomena. In this work, the revealing properties of metal (Na/Mg/Al)-adsorbed graphene systems are investigated by means of the first-principles method. The single- and double-sided chemisorption cases, the various adatom concentrations, the hollow/top/valley/bridge sites, and the buckled structures are taken into account.

Featured properties of Li-based battery anode: LiTiO.

3D ternary LiTiO, a Li-based battery anode, presents an unusual lattice symmetry (triclinic crystal), band structure, charge density, and density of states under first-principles calculations. It is a large direct-gap semiconductor with ∼ 2.98 eV.

Rich Magnetic Quantization Phenomena in AA Bilayer Silicene.

The rich magneto-electronic properties of AA-bottom-top (bt) bilayer silicene are investigated using a generalized tight-binding model. The electronic structure exhibits two pairs of oscillatory energy bands for which the lowest conduction and highest valence states of the low-lying pair are shifted away from the K point. The quantized Landau levels (LLs) are classified into various separated groups by the localization behaviors of their spatial distributions.