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We report a detailed analysis of the crystal structure, electronic structure, and thermoelectric (TE) properties of a stoichiometric Mn2CoAl inverse full-Heusler alloy, which has been predicted to ...

A number of technologies would benefit from developing inorganic compounds and materials with specific electronic and magnetic exchange properties. Unfortunately, designing compounds with these properties is difficult because metal⋅⋅⋅metal coupling schemes are hard to predict and control. Fully characterizing communication between metals in existing compounds that exhibit interesting properties could provide valuable insight and advance those predictive capabilities. One such class of molecules are the series of Lindqvist iron-functionalized and hexavanadium polyoxovanadate-alkoxide clusters, which we characterized here using V K-edge X-ray absorption spectroscopy. Substantial changes in the pre-edge peak intensities were observed that tracked with the V 3d-electron count. The data also suggested substantial delocalization between the vanadium cations. Meanwhile, the FeIII cations were electronically isolated from the polyoxovanadate core.

Two-dimensional (2D) van der Waals (vdw) heterojunction devices exploiting unique physical properties are the backbone of new electrical, magnetic, and optical sensing technologies, a key advantage...

A new terbium (III) luminescent compound {[Tb2(PDC)2(ox)(H2O)4](H2O)2}n was synthesized by the self-assembly of Tb3+ ions with 3,5-pyridinedicarboxylate (PDC) and oxalate (ox) ligands and characterized by fluorescence spectroscopy and single-crystal X-ray diffraction. The density functional theory (DFT) and high-level correlated abinitio wave function methods with Spin-Orbit Coupling correction (CASSCF/SO and CAS-NEVPT2/SOC) were successfully applied to predict the absorption and emission spectra of this strongly correlated lanthanide system in excellent agreement with the experimental results.

In order to explore Si-related spintronic materials, we use a full-potential density-functional-theory method to study electronic structure and magnetic properties of EuFe 2 Si 2 with the layered ThCr 2 Si 2 structure. Our comparative optimization investigation among 25 magnetic configurations reveals that its ground state phase is a ferrimagnet, in which the spins in both of Eu and Fe layers are aligned ferromagnetically, but the Eu spins are aligned antiferromagnetically with the Fe spins. This is very different from the striped antiferromagnetic ground state for the Fe spins in FeAs-based materials. The filled Eu 4f bands in the majority-spin channel, very flat, are just below the Fermi level and the Fe 3d bands cover an energy range of 4 eV astride the Fermi level. The Eu atom is ionic and contributes a moment of nearly 7 μ B , and Fe is bonded strongly with Si, which results in a low-moment state for Fe. Our results are of interest to explore the physical properties of the Fe-based materials, and can stimulate further effort to seek useful Si-related spintronic materials.

Heterogeneous metal interfaces play a key role in determining the mechanism and performance of catalysts. However, in situ characterization of such interfaces at the molecular level is challenging. Herein, two model interfaces, Pd and Pt overlayers on Au single crystals, were constructed. The electronic structures of these interfaces as well as effects of crystallographic orientation on them were analyzed by shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) using phenyl isocyanide (PIC) as a probe molecule. A clear red shift in the frequency of the C≡N stretch (νNC ) was observed, which is consistent with X-ray photoelectron spectroscopy (XPS) data and indicates that the ultrathin Pt and Pd layers donate their free electrons to the Au substrates. Furthermore, in situ electrochemical SHINERS studies showed that the electronic effects weaken Pt-C/Pd-C bonds, leading to improved surface activity towards CO electrooxidation.

Unraveling the specific structures of transition metal polyborides is critical for understanding their underlying physical and electronic properties. Using an ab initio particle swarm optimization algorithm for the crystal structure determination, we have predicted the monoclinic C 2 / c and Amm2 phases as the stable structures for NbB4. It is firstly found that the C 2 / c phase transforms to Amm2 phase at about 42 GPa. Intriguingly, both phases are dynamically and mechanically stable at the ambient conditions. Furthermore, both phases of NbB4 have high bulk and shear moduli and a low Poisson's ratio and can be classified as ultra-incompressible materials. Besides, the strong covalent bonding nature of NbB4 polymorphs was confirmed by the ELF analysis. We hope that these findings will stimulate experimental work on synthesis of this technologically important material.

In heterogeneous catalysis, characterization of heterogeneous metal interfaces of bimetallic catalysts is a crucial step to elucidate the catalytic performance and is a key to develop advanced catalysts. However, analytical techniques such as X-ray photoelectron spectroscopy can only work in vacuum conditions and are difficult to use for in situ analysis. Here, we present efficient and convenient core–shell nanoparticle-enhanced Raman spectroscopy to explore the in situ electronic structures of heterogeneous interfaces (Au@Pd and Au@Pt core–shell NPs) by varying the shell thickness. The experimental observations reported here clearly show that Pd donates electrons to Au, while Pt accepts electrons from Au at the heterogeneous interfaces. This conclusion gains further support from ex situ X-ray photoelectron spectroscopy results. The Au core greatly affects the electronic structures of both the Pd and Pt shells as well as catalytic behaviors. Finally, the as-prepared core–shell nanoparticles were used to d...

We study the geometric and electronic properties of germanene adsorbed with several small organic molecules (SOMs) by using first-principles calculations. The adsorption energies are found in the range from −0.459 to −0.231 eV, higher than those of SOMs adsorbed on graphene and silicene, indicating strong interactions between organic molecules and germanene. These lead to a large enhancement of band gap of germanene with sizable values of 3.9–81.9 meV due to the sublattice symmetry breaking. Noticeably, the characteristics of Dirac cone with low effective mass and high electron mobility are preserved. These findings provide a possible way to design germanene based optoelectronic devices.

By means of state-of-the-art density functional theory (DFT) computations, we systematically studied the structural, electronic, and optical properties of a novel two dimensional material, namely stanane (SnH). According to our computational results, stanane is semiconducting with a direct band gap of 1.00 eV, which can be flexibly tuned by applying an external strain. Remarkably, stanane has much higher electron and hole mobilities than those of a MoS2 monolayer at room temperature. Moreover, stanane has rather strong optical absorption in the visible as well as infrared regions of the solar spectrum. These results provide many useful insights for the wide application of stanane in electronics and optoelectronics.

Modifying the surface energetics, particularly the work function of advanced materials, is of critical importance for a wide range of surface- and interface-based devices. In this work, using in situ photoelectron spectroscopy, we investigated the evolution of electronic structure at the SrTiO3 surface during the growth of ultra-thin MoO3 layers. Because of the large work function difference between SrTiO3 and MoO3, the energy band alignment on the SrTiO3 surface is significantly modified. The charge transfer and dipole formation at the SrTiO3-MoO3 interface leads to a large modulation of work function and to apparent doping in SrTiO3. The measured evolutions of electronic structure and upward band bending suggest that the growth of ultra-thin MoO3 layers is a powerful tool with which to modulate the surface energetics of SrTiO3, and this surface engineering approach could be generalized to other functional oxides.

The electronic structure of InN nanosheets doped by light elements (Be, B, C, and O) is studied based on spin-polarized density functional theory within the generalized gradient approximation. The results show that the Be and C dopants in InN nanosheets induce spin polarized states in the band gap, or near the valence band, which generates local magnetic moments of 1.0 µB with one dopant atom. Due to the exchange spin-splitting, the three 2p electrons of Be atom are all in px and py orbitals (↑↑↓). So Be will coordinate with host atoms by σ coordination bond. The long-range ferromagnetic order above room temperature is attributed to p–p coupling. For C atom, the configuration of the five 2p electrons is (↑↑↑↓↓), and the unpaired electron is in pz(↑) orbital. So the π bond will be formed between C atom and other atoms. Due the weak π bond cannot support long-range coupling, no stable magnetism is sustained if two C dopants are separated by longer than 3.58 A.

Based on first-principles calculations, we study the electronic structure, magnetic properties and optical properties of transition metal (TM) doped SnO2NSs. Computational results indicate that pristine SnO2NSs is a direct gap semiconductor with nonmagnetic states. Cr, Mn, Fe atom doping can induce 2μB, −3μB and 2μB magnetic moment, respectively, while Ni atom doped SnO2NSs keeps the nonmagnetic states. More interestingly, Fe doped SnO2NSs becomes an indirect gap semiconductor, and the Cr, Mn and Ni atom doping maintain the character of direct gap semiconductor. For optical properties, the optical absorption edge shows red shift phenomenon for a TM atom (Cr, Mn, Fe or Ni) doped SnO2NSs. In addition, the tensity of absorption, reflection and refraction coefficient are enhanced significantly in the visible light region, which may be very useful for the design of solar cells, photoelectronic devices and photocatalysts.

We investigated highly efficient phosphorescent organic light-emitting diodes (PHOLEDs) based on three novel 1,3,5-triazine derivatives as the host materials and two kinds of iridium complexes as the guests, respectively. For comparison, the devices using a common phosphorescent host 4,4′-N,N′-dicarbazolebiphenyl (CBP) have also been fabricated. Results show that the devices using 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (PTC) and 4-(4,6-diphenoxy-1,3,5-triazin-2-yl)-N,N-diphenylaniline (POTA) as host have better performance than that of CBP. In comparison with the PHOLEDs based on CBP host, PTC- and POTA-based PHOLEDs show significantly lower driving voltages and higher power efficiencies. The high bipolar carrier mobility of the host is found to be critical to this kind of doping system, which would balance the injection of both carriers and improve efficiency.

The bonding nature of CF3AuCO and its clusters [CF3AuCO]n (n = 2–4) (Angew. Chem., Int. Ed. 2011, 50, 6571) have been theoretically investigated with density functional theory (B3LYP, B3LYP-D3, M06-2X, M06-2X-D3, M05-2X, M06L, B3PW91), the Hartree–Fock method (HF), second-order Moller–Plesset perturbation theory (MP2), and the coupled cluster method with perturbative triplets (CCSD(T)) using a series of basis sets. For comparison, larger complexes that have been studied experimentally, [Mes3PAuCO]+ and [SIDippAuCO]+, were also computed. Various ligands as well as their gold clusters [RAuL]2–4 (R = OB, Br, Cl, CH3, HCC; L = CO, N2, OB) were also investigated. The Au–CO bonds consist of electrostatic attraction, Au←CO donation, and Au→CO π-back-bonding components. The LMOEDA results show that the major contributors of RAuL are found to be electrostatic, which linearly correlates with the interaction energy. Electrostatic stabilization is mainly responsible for aurophilic interactions in the formation of CF3...

The electronic structures and elastic anisotropies of cubic Ti3AlN, Zr3AlN, and Hf3AlN are investigated by pseudopotential plane-wave method based on density functional theory. At the Fermi level, the electronic structures of these compounds are successive with no energy gap between conduct and valence bands, and exhibit metallicity in ground states. In valence band of each partial density of states, the different orbital electrons indicate interaction of corresponding atoms. In addition, the anisotropy of Hf3AlN is found to be significantly different from that of Ti3AlN and Zr3AlN, which involve the differences in the bonding strength. It is notable that Hf3AlN is a desired thermal barrier material with the lowest thermal conductivity at high temperature among the three compounds.

The dissociation of SO 3 molecules on the walls of armchair ( m , m ) ( m = 3, 5) and zigzag ( n , 0) ( n = 5–10) single-wall carbon nanotubes (SWCNTs) was investigated using first-principles calculations. The calculated reaction enthalpies and energy barriers show a nearly linear decrease with decreasing tube diameter. Our results indicate that the dissociation of SO 3 on the walls of SWCNTs is strongly dependent on the tube diameter for the selective etching of SWCNTs with small diameters ( d 3 . Our study sheds light on effective separation of SWCNTs for their practical application in many fields.

Structural, electronic and optical properties have been calculated for Tin dioxide nanoribbons (SnO2 NRs) with both zigzag and armchair shaped edges by first principle spin polarized total energy calculation. We find that both zigzag and armchair SnO2NR have indirect band gaps. The band gap oscillates between the maximum of 3.38 eV and the minimum of 1.69 eV and eventually levels off to a value of 2.09 eV for armchair nanoribbons, while for zigzag nanoribbons, the band gap oscillates between the maximum of 2.25 eV and the minimum of 2.04 eV and eventually levels off to 2.18 eV. Our investigation further reveals that the optical absorption capacity enhanced with increasing ribbon width for both Z-SnO2NRs and A-SnO2NRs. More interestingly, when introducing Ag impurities, the optical absorption edge shifts to the low energy region. These findings can be a useful tool for the design of a new generation of materials with improved solar radiation absorption.

The successful synthesis and outstanding properties of graphene have promoted strong interest in studying hypothetical graphene-like silicon sheet (silicene). Very recently, 2D silicon nanosheet (Si-NS) stabilized by hexyl groups was reported in experiment. We here present an atomic-level investigation of the geometric stability and electronic properties of Si-NS by density functional calculations and molecular dynamics simulations. The most stable structure of the hexyl-modified Si-NS corresponds to the one in which the hexyl groups are regularly attached to both sides of the sheet, with the periodicity of the hexyl groups on the sheet being 7.17 A, in good agreement with the experimental value of 7.1 A. The electrostatic repulsion effect of the hexyl groups could be an important reason for the favorable structure. The electronic structure of the hexyl-modified Si-NS shows a direct band gap that is not sensitive to the length of the alkyl group but sensitive to the strain effect, which can be used to tun...

The optical properties of face-centered cubic IVB group transition metal nitrides such as TiN, ZrN, and HfN were calculated using the plane wave pseudopotential method based on first-principle density function theory. The results of band structures show that conduction bands are mainly formed by the metal atom d-state, whereas valence bands are mainly formed by the N 2p-state. In optical properties research, the computed results of complex dielectric functions, absorptions, reflectivities, conductivities and loss functions of the three materials are analysed in terms of band structures. The results agree with experiment data. Analysis results show that the optical properties of these materials in low-energy regions are metallic because of the free electrons intraband-transition, and the transit to semiconducting properties in high-energy area is caused by valence electrons interband-transition. The sharp peaks of the transmissivity spectra indicate excellent optical selectivity in the visible light area. Moreover, lowering the starting energies of interband-transitions as a possible method to improve optical selectivities is discussed

Based on first-principles calculations, we have investigated the electronic structure and magnetic properties of the fully-hydrogenated ZnO nanosheet (ZnONS) doped with B, C, N, and F atoms. The results show that p-type doped ZnONSs exhibit magnetic behaviors due to less electronegative p-type dopant than substituted oxygen atom, while n-type doping results in nonmagnetic states. More interestingly, B and C doped ZnONSs exhibit half-metallic behaviors with 100% spin-polarized current at the Fermi level. The long-range ferromagnetic order above room temperature, attributed to p–p coupling chain between two dopants, is also observed. It is expected that the physical understanding of ferromagnetic order would direct experiments to synthesize the novel ZnO-based nanostructures in spintronics.

NSFC [20620130427]; MOST [2007DFC 40440]; National Basic Research Program of China [2009CB930703, 2007CB815303]

Using density functional theory and nonequilibrium Green’s function (NEGF) formalism, we have theoretically investigated the magnetic and transport property of graphene by introducing dopant and defect. While the quasi-linear energy dispersion near the Dirac point remains and no magnetic property appears, graphene of p-type doping and n-type doping can be induced through doping with B and N atoms, respectively. It demonstrates that vacancy or metal doping can induce spontaneous magnetization. The current versus voltage simulation reveals device based on the N-doped graphene could have much higher conductance than that using pristine or B-doped graphene.

The ground structure, elastic and electronic properties of several phases of NbN are determined based on ab initio total-energy calculations within the framework of density functional theory. Among the five crystallographic structures that have been investigated, the hexagonal phases have been found to be more stable than the cubic ones. The calculated equilibrium structural parameters are in good agreement with the available experimental results. The elastic constants of five structures in NbN are calculated, which are in consistent with the obtained theoretical and experimental data. The corresponding Debye temperature and elastic ansitropies are also obtained. The Debye temperature of NbN in various structures consistent with available experimental and theoretical data, in which the Debye temperature of δ-NbN is highest. The anisotropies of ZB-NbN, NaCl-NbN, CsCl-NbN gradually increases. For hexagonal structure, the anisotropies of ε-NbN are stronger than that of δ-NbN. The electronic structures of NbN under pressure are investigated. It is found that NbN have metallization and the hybridizations of atoms in NbN under pressure become stronger.

Electronic structure and magnetism of Co-doped (110) SnO 2 surface are investigated using the full-potential linearized augmented plane-wave method. Total energy calculations indicate that Co atoms prefer to surface sites and couple ferromagnetically when they occupy nearest-neighbor sites. Irrespective of the sites that Co dopants occupy, different geometries with ferromagnetic, antiferromagnetic, and nonmagnetic configurations are predicted in Co-doped systems, which provide a key to understand seemingly conflicting experimental results.

In order to exploit the potential applications of graphene as gas sensors, the adsorptions of a series of small gas molecules (such as CO, O2, NO2 and H2O) on pristine graphene (PG) and Si-doped graphene (SiG) have been investigated by ab initio calculations. Our results indicate that the electronic properties of PG are sensitive to O2 and NO2 molecules, but not changed much by the adsorption of CO and H2O molecules. Compared with PG, SiG is much more reactive in the adsorption of CO, O2, NO2 and H2O. The strong interactions between SiG and the adsorbed molecules induce dramatic changes to the electronic properties of SiG. Therefore, we suggest that SiG could be a good gas sensor for CO, O2, NO2 and H2O.

Based on the pseudo potential plane-wave method of density functional theory (DFT), Ti1−x Nb x Al ( x =0, 0.062 5, 0.083 3, 0.125, 0.250) crystals’ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M (M=Ti, Al) and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAlNb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%–12.5% (mole fraction).

We have performed ab initio calculations on the stability and structural and electronic properties of the fullerene-like cage (SiC)12 and its derivative products, the (SiC)12–(SiC)12 dimers and (SiC)12-based nanowires. The (SiC)12–(SiC)12 dimers and (SiC)12-based nanowires are found more stable than the (SiC)12. The optimized configurations of the (SiC)12-based nanowires are especially regular and exhibit stable dumbbell-shaped chain structures. The electronic structure calculations indicate that the two novel (SiC)12-based nanowires have band gaps of 1.586 eV and 2.055 eV, respectively, which may be promising for application in nanotechnology.

We performed ab initio calculations on the cytosine-functionalized silicon-doped single walled carbon nanotubes (SWNT). The results show that silicon substitutional doping to SWNT can dramatically change the atomic and electronic structures of the SWNT. And more importantly, it may provide an efficient pathway for further sidewall functionalization to synthesize more complicated SWNT based complex materials, for example, our previously proposed base-functionalized SWNTs, because the doping silicon atom can improve the reaction activity of the tube at the doping site due to its preference to form sp3 hybridization bonding.

We have investigated the electronic structures of C-doped (9,0) boron nitride nanotubes (BNNTs) and hydrogen-decorated C-doped (9,0) BNNTs using density functional theory (DFT). It is found that the doping effect of C-doped BNNTs can be compensated by adsorption of H atom on the C sites. The adsorption energies for hydrogen atoms on different adsorption sites on BNNTs and C-doped BNNTs are obtained by using ONIOM method. The results indicate that the most favorable configuration of the adsorption structures is a hydrogen atom adsorbed on the C site of C-doped BNNT.

In the framework of single-electronic tight-binding nearest-interaction transfer model, after establishing the method of constructing a class of two-dimensional SML quasilattices, we have studied the spectral properties of two-dimensional SML quasilattices by means of a decomposition–decimation method based the renormalization-group technique. It is found that the spectra have a variety of multifurcating structures, the total spectra are symmetrical, and every spectral line splits into odd sub-bands in the higher hierarchy. The analytic results show that under the first approximation, there exist only six kinds of clusters and the bare energy splits into thirteen subbands, and under the second approximation, several kinds of new spitting manners occur, e.g., 1:33, 1:19. The analytical results are confirmed by numerical simulations.

Remarkable power conversion efficiencies (PCE) of metal–halide perovskite solar cells (PSCs) are overshadowed by concerns about their ultimate stability, which is arguably the prime obstacle to commercialization of this promising technology. Herein, the problem is addressed by introducing ethane-1,2-diammonium (+NH3(CH2)2NH3+, EDA2+) cations into the methyl ammonium (CH3NH3+, MA+) lead iodide perovskite, which enables, inter alia, systematic tuning of the morphology, electronic structure, light absorption, and photoluminescence properties of the perovskite films. Incorporation of

We use the state-of-the-arts density-functional-theory method to study various magnetic orders and their effects on the electronic structures of the FeSe. Our calculated results show that, for the spins of the single Fe layer, the striped antiferromagnetic orders with distortion are more favorable in total energy than the checkerboard antiferromagnetic orders with tetragonal symmetry, which is consistent with known experimental data, and the inter-layer magnetic interaction is very weak. We investigate the electronic structures and magnetic property of the distorted phases. We also present our calculated spin coupling constants and discuss the reduction of the Fe magnetic moment by quantum many-body effects. These results are useful to understand the structural, magnetic, and electronic properties of FeSe, and may have some helpful implications to other FeAs-based materials.

The structural parameters, elastic constants and electronic structure of NbB(2) under pressure are investigated by using first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA). The obtained results are in agreement with the available theoretical data. It is found that the elastic constants and the Debye temperature of NbB(2) increase monotonically and the anisotropies weaken with pressure. The band structure and density of states (DOS) of NbB(2) under pressure are also presented. It is the sigma hole that determines the superconductivity in NbB(2), and the features of the sigma bands are unchanged after applying pressure except for a shift of position. The density of states (DOS) at the Fermi level decreases with increasing pressure, in conjunction with Bardeen Cooper-Schrieffer (BCS) theory, which can predict T(c) decreasing with pressure, in agreement with the trend of the theoretical T(c) versus pressure.

Herein, we describe the molecular electronic structure, optical, and charge-transport properties of anthracene derivatives computationally using density functional theory to understand the factors responsible for the improved efficiency and stability of organic light-emitting diodes (OLEDs) with triphenylamine (TPA)-substituted anthracene derivatives. The high performance of OLEDs with TPA-substituted anthracene is revealed to derive from three original features in comparison with aryl-substituted anthracene derivatives: 1) the HOMO and LUMO are localized separately on TPA and anthracene moieties, respectively, which leads to better stability of the OLEDs due to the more stable cation of TPA under a hole majority-carrier environment; 2) the more balanceable hole and electron transport together with the easier hole injection leads to a larger rate of hole-electron recombination, which corresponds to the higher electroluminescence efficiency; and 3) the increasing reorganization energy for both hole and electron transport and the higher HOMO energy level provide a stable potential well for hole trapping, and then trapped holes induce a built-in electric field to prompt the balance of charge-carrier injection.

Using a single-particle atomistic pseudopotential method followed by a many-particle configuration interaction method, we investigate the geometry, electronic structure and optical transitions of a self-assembled InAs/GaAs quantum ring (QR), changing its shape continously from a lens-shaped quantum dot (QD) to a nearly one dimensional ring. We find that the biaxial strain in the ring is strongly asymmetric in the plane perpendicular to the QR growth direction, leading to giant optical anisotropy.

We investigate the electronic structure of the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ quantum dots using an atomistic pseudopotential method and compare it to that of the $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots (QDs). We show that even though the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ and $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots have the same dot material, their electronic structures differ significantly in certain aspects, especially for holes: (i) The hole levels have a much larger energy spacing in the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ dots than in the $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots of corresponding size. (ii) Furthermore, in contrast with the $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots, where the sizable hole $p$, $d$ intrashell level splitting smashes the energy level shell structure, the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ QDs have a well defined energy level shell structure with small $p$, $d$ level splitting, for holes. (iii) The fundamental exciton energies of the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ dots are calculated to be around $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ $(\ensuremath{\sim}1.55\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$, about $200\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ lower than those of typical $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ QDs, mainly due to the smaller lattice mismatch in the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ dots. (iv) The widths of the exciton $P$ shell and $D$ shell are much narrower in the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ dots than in the $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots. (v) The $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ and $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ dots have a reversed light polarization anisotropy along the [100] and $[1\overline{1}0]$ directions.

Four well-resolved peaks with very narrow linewidths were found in the D-band and G-band features of double-walled carbon nanotubes DWNTs. This fact implies the occurrence of additional van Hove singularities vHSs in the joint density of states JDOS of DWNTs, which is consistent with theoretical calculations. According to their peak frequencies and theoretical analysis, the two outer peaks can be deduced to originate from a strong coupling between the two constituent tubes of commensurate DWNTs and the two inner peaks were curvature-related and assigned to originate from the two tubes with a weak coupling. This observation and elucidation constitute the first Raman evidence for atomic correlation and the resulting electronic structure change of the two constituent tubes in DWNTs. This result opens the possibility of predicting and modifying the electronic properties of DWNTs for their electronic applications.

The electronic structure and optical properties of Mn and B, C, N co-doped molybdenum disulfide (MoS2) monolayers have been investigated through first-principles calculations. It is shown that the MoS2 monolayer reflects magnetism with a magnetic moment of 0.87 μB when co-doped with Mn-C. However, the systems co-doped with Mn-B and Mn-N atoms exhibit semiconducting behavior and their energy bandgaps are 1.03 and 0.81 eV, respectively. The bandgaps of the co-doped systems are smaller than those of the corresponding pristine forms, due to effective charge compensation between Mn and B (N) atoms. The optical properties of Mn-B (C, N) co-doped systems all reflect the redshift phenomenon. The absorption edge of the pure molybdenum disulfide monolayer is 0.8 eV, while the absorption edges of the Mn-B, Mn-C, and Mn-N co-doped systems become 0.45, 0.5, and 0 eV, respectively. As a potential material, MoS2 is widely used in many fields such as the production of optoelectronic devices, military devices, and civil devices.

We have studied the atomic and electronic structures, as well as the self-assembly mechanism of cytosine $(C)$ and guanine $(G)$ functionalized single-walled carbon nanotubes (SWNTs) by using ab initio calculations combined with empirical molecular dynamics (MD) simulations. Our results show that both the atomic and electronic structures of the SWNT can be drastically changed by the decoration with these bases, suggesting an effective pathway for band structure engineering. More interestingly, these functionalized SWNTs display self-assembly character and tend to form a ``ladder'' configuration as revealed in the MD simulations, which may find wide applications in fabricating nanodevices and nanocircuits.

We perform density functional calculations for the geometrics, strain energy, and electronic structures of silicon carbide nanotubes ($\mathrm{SiCNT}$'s). We find that the strain energy in $\mathrm{SiCNT}$'s is as higher as $0.686\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{atom}$ relative to $3\mathrm{C}\text{\ensuremath{-}}\mathrm{SiC}$ for (5,5) $\mathrm{SiCNT}$ and decreases with increasing tube diameter. All the $\mathrm{SiCNT}$'s are semiconductors, the band gap of which increases with increasing tube diameter. In contrast to $3\mathrm{C}\text{\ensuremath{-}}\mathrm{SiC}$, zigzag $\mathrm{SiCNT}$ has a direct band gap at the $\ensuremath{\Gamma}$ point, whereas armchair and chiral tubes have an indirect band gap. The highest occupied valance band and the lowest unoccupied conduction band highly localize to $\mathrm{C}$ and $\mathrm{Si}$ atoms, respectively. Hydrogen-decorated $\mathrm{SiCNT}$'s display the characters of $p$- or $n$-type semiconductors depending on the adsorbing site.

First-principles calculations are performed to study the structural, electronic and magnetic properties of Co-doped SnO2 nanosheets (NSs), using the generalized gradient approximation (GGA) plus Hubbard U method. We find that two Co atoms have a clustering tendency and the magnetic interactions between them exhibit a ferromagnetic (FM) coupling, while the appearance of an oxygen vacancy (VO) turns it into an antiferromagnetic (AFM) order. When the Li atom is codoped into Co-doped SnO2NS, the interactions between Co atoms are rehabilitated to FM coupling with a high Curie temperature (TC) of 850 K. The electronic structure analysis reveals that this is mainly attributed to the hole-induced double-exchange mechanism from s–d hybridizations between Li and Co, which finally activates a long-range FM coupling between two Co atoms. These findings could be very useful in nano-material design for spintronics.

We have carried out first-principles calculations to explore the adsorption and diffusion of Au adatoms on boron nitride nanoribbons (BNNRs). We found that Au adatoms prefer to locate at the edge B site of the ribbons for both armchair (A-) and zigzag (Z-) BNNRs. Different diffusion paths, such as diffusion from central region to edge site, along the subedge sites or along the edge sites, are considered. The unique atomic arrangement and electronic structures of Z-BNNRs make the Au adatom tend to migrate only to B edge site rather than to the both edges. Different from the cases of graphene nanoribbons, the energy barriers for A-BNNRs are higher than those of the corresponding paths for Z-BNNRs. The electronic structure calculations indicate the wide-band-gap features are preserved in the Au-doped BNNRs as the Au concentration is low. With the increase of Au concentration, the Au adatoms form an atomic chain along the B zigzag edge, resulting in band gap closure. These results are expected to provide usef...

We present a detailed density-functional calculation for multielectron bubbles with charges {ital z}{le}50. The calculation is similar to that for metal clusters, but we found no obvious shell structure in the charged bubbles. The exchange-correlation interaction has the important effect of reducing the bubble radius and, hence, enhances its stability. A simple but useful analysis is introduced, which explains the calculated results and could also work for large-{ital z} bubbles. The calculated mobilities of bubbles agree well with the measured values but, quite surprisingly, the results indicate that the {ital z}=3 bubbles have not been observed experimentally.

Ab initio calculations were conducted to investigate the electronic structures and magnetic properties of fluorinated boron nitride nanotube (F-BNNT). It was found that the chemisorption of F atoms on the B atoms of BNNT can induce spontaneous magnetization, whereas no magnetism can be produced when the B and N atoms are equally fluorinated. This provides a different approach to tune the magnetic properties of BNNTs as well as a synthetic route toward metal-free magnetic materials.