Spatial Distribution Of Charge Density Research Articles

Electric-field-driven ferromagnetic response in Janus MnReX3 (X = Se, S) monolayer via asymmetric interface orbital hybridization

Abstract Regulating spin-related electronic structures of two dimensional (2D) materials by an external electric field plays a substantial role in achieving spintronic and multistate information storage. However, electric-field-dependent ferromagnetic behavior at atomic-thick 2D materials is very difficult to be realized due to their intrinsic inversion symmetry, in which the symmetric spatial distribution of charge density makes it become insensitive to spontaneous polarization from external electric field. Herein, a new-type Janus MnReX3 (X = Se, S) monolayer with noncentrosymmetric configuration in which their orbital hybridization at internal interface can be engineered by rearranging the spatial symmetry of out-of-plane charge density. As a result, the spin exchange interaction among magnetic sites can be regulated by the electric-field-driven charge density redistribution, leading to a controllable ferromagnetic behavior at room temperature. Our results not only suggest a promising strategy to regulate the ferromagnetic response by reducing the crystal symmetry, but also provide a new insight into designing 2D magnetic materials.

Feature-rich electronic properties of three-dimensional ternary compound: Li7P3S11

PurposeThe theoretical findings serve as a foundation for further research into understanding sulfide-based solid-state electrolytes, ultimately advancing the progress of all-solid-state batteries.Design/methodology/approachThe electronic properties of Li7P3S11 are thoroughly explored through first-principles calculations.FindingsThis investigation encompasses the intricate atom-dominated valence and conduction bands, spatial charge density distribution and the breakdown of atom and orbital contributions to van Hove singularities. Additionally, the compound’s wide and discrete energy spectra reflect the substantial variations in bond lengths and its highly anisotropic geometric structure. The complex and nonuniform chemical environment indicates the presence of intricate hopping integrals.Originality/valueThis study provides valuable insights into the critical multiorbital hybridizations occurring in the Li-S and P-S chemical bonds. To validate the theoretical predictions, experimental techniques can be employed. By combining theoretical predictions with experimental data, a comprehensive understanding of the geometric and electronic characteristics of Li7P3S11 can be achieved.

FRACTAL MODEL OF FLOW CURRENT IN MICRO ROUGH CAPILLARY TUBES

Based on the fractal geometry science and the model of flow friction resistance when fluid flows through rough microcapillaries, the formula of diffusion layer thickness and the spatial charge density distribution of the pipe were derived. The relationship between the amount of space charge and the structural parameters of rough elements, relative roughness, liquid conductivity, pipeline diameter, and other physical quantities was discussed. It was found that the height of rough elements is directly proportional to the thickness of the diffusion layer, and also positively proportional to the amount of current. The predicted results of the model are in good agreement with existing models and various published experimental data, verifying the accuracy and reliability of the model.

Diverse structural and electronic properties of carbon-substituted armchair silicene nanoribbons: A first-principles study

The structural and electronic properties of the armchair silicene nanoribbons (ASiNRs) under various C substitutions are investigated using the first-principles calculations. The C substitution-diversified structural and electronic properties are fully identified by the developed first-principles quantities, including the formation energies, phonon calculations, optimal structural parameters, orbital- and atom-projected density of states, and direction-projected spatial charge density distributions. The C substitutions at various adatom concentrations and distributions form the typical C substitution configurations of the single C, ortho-2C, meta-2C, para-2C, and 100% C, whereas the lower buckling height is found at the higher concentrations that become the flat 1D structure at 100% C substitution. The reshaped bandgaps are larger under shorter Si–C bond lengths. The largest opened bandgap of 2.37 eV is found at the highest adatom concentration of the 100% C configuration. The C substitutions generate the quasi σ bonds of the Si-(3s, 3p x , and 3p y ) and C-(2s, 2p x , and 2p y ) orbitals and the quasi π bonds of the Si-3p z and C-2p z orbitals, in which the quasi π orbitals create the long-range quasi π bands that determine the reshaped bandgaps. The quasi σ and π orbitals are hybridized at the middle valence energies that only separate at the deeper valence energies. The weak separation of the σ and π orbitals is responsible for the hybridization mechanism of the mixed sp 2 /sp 3 quasi in the C-substituted systems. The diverse electronic properties of the C-substituted ASiNRs will be very compatible with electronic and optoelectronic applications.

Diverse Properties of Carbon-Substituted Silicenes

The theoretical framework, which is built from the first-principles results, is successfully developed for investigating emergent two-dimensional materials, as it is clearly illustrated by carbon substitution in silicene. By the delicate VASP calculations and analyses, the multi-orbital hybridizations are thoroughly identified from the optimal honeycomb lattices, the atom-dominated energy spectra, the spatial charge density distributions, and the atom and orbital-decomposed van Hove singularities, being very sensitive to the concentration and arrangements of guest atoms. All the binary two-dimensional silicon-carbon compounds belong to the finite- or zero-gap semiconductors, corresponding to the thoroughly/strongly/slightly modified Dirac-cone structures near the Fermi level. Additionally, there are frequent π and σ band crossings, but less anti-crossing behaviors. Apparently, our results indicate the well-defined π and σ bondings.

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, 3s2, and (3s2, 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. The hollow and valley adsorptions that correspond to the Na/Mg and Al cases, respectively, create extremely nonuniform environments. This leads to diverse orbital hybridizations in Na/Mg/Al–Si bonds, as indicated by the Na/Mg/Al-dominated bands, as well as the spatial charge density distributions and the orbital-projected density of states (DOS). Out of three types of metal-adatom adsorptions, the Al-adsorption configurations produce the strongest chemical modifications. The ferromagnetic configurations have been shown to survive only in specific Mg and Al adsorptions, but not in the Na cases. The presented theoretical predictions could be verified experimentally, and potential applications are discussed. Additionally, important similarities and differences with graphene-related systems are examined.

Modelling a capped carbon nanotube by linear-scaling density-functional theory

The apex region of a capped (5,5) carbon nanotube (CNT) has been modelled with the DFT package ONETEP, using boundary conditions provided by a classical calculation with a conducting surface in place of the CNT. Results from the DFT solution include the spatial distribution of charge density, the changes to the highest occupied molecular orbital (HOMO) induced by an external field and a comparison of calculations of total potential energy E with and without exchange-correlation energy EXC. The contribution to the work function from exchange and correlation effects is found to be nearly as much again as that from a purely electrostatic calculation.

Concentration-Diversified Magnetic and Electronic Properties of Halogen-Adsorbed Silicene

Diverse magnetic and electronic properties of halogen-adsorbed silicene are investigated by the first-principle theoretical framework, including the adatom-diversified geometric structures, atom-dominated energy bands, spatial spin density distributions, spatial charge density distributions and its variations, and orbital-projected density of states. Also, such physical quantities are sufficient to identify similar and different features in the double-side and single-side adsorptions. The former belongs to the concentration-depended finite gap semiconductors or p-type metals, while the latter display the valence energy bands with/without spin-splitting intersecting with the Fermi level. Both adsorption types show the halogen-related weakly dispersed bands at deep energies, the adatom-modified middle-energy σ bands, and the recovery of low-energy π bands during the decrease of the halogen concentrations. Such feature-rich band structures can be verified by the angle-resolved photoemission spectroscopy experiment.

Two-proton radioactivity with 2p halo in light mass nuclei A = 18–34

Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A=18–34. We predict 19Mg, 22Si, 26S, 30Ar and 34Ca as promising candidates of ground state 2p-radioactivity with S2p<0 and Sp>0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound 22Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.

Crystal structure and bonding characteristics of transformation products of bcc β in Ti-Mo alloys

Abstract Rietveld analysis of X-ray diffraction patterns of α′, α″ and β phases of four alloys of Ti-Mo has been carried out to refine their crystal structures and understand their nature of bonding. The addition of molybdenum to titanium is found to shift the stability of crystal structure from hcp to orthorhombic to bcc, as expected. The unit cell dimensions and the atomic positions of α′, α″ and β phases were evaluated, with excellent reliability indices. The reduction in unit cell dimensions and its volume, bond length and co-ordination number with addition of molybdenum is consistent with the reduced size of solute atom. The orthorhombic α″ phase, a transition phase with a minor distortion of hcp α′, is found to be closer to α′ than β phase, based on the orthorhombicity (b/a) and the volume of equivalent orthorhombic unit cells of the phases and the atomic shuffle y in 4c Wyckoff positions along b axis of α″ phase. The Fourier electron density contour maps suggest that the bonding in all phases is predominantly metallic. However, addition of molybdenum delocalizes the spatial distribution of charge density, suggesting an enhancement of metallic character. Anisotropy in charge density was observed along 〈011〉 and 〈010〉 in (100), 〈101〉 and 〈001〉 in (010) and 〈110〉 and 〈010〉 in (001) plane. This offers direct evidence for the origin of anisotropy in the values of elastic constants, reported in literature.

Structural characterization and electron density distribution studies of (La0.8Ca0.2)(Cr0.9−xCo0.1Mnx)O3

The doped lanthanum chromite (La0.8Ca0.2)(Cr0.9−xCo0.1Mnx)O3 (x=0.03, 0.06, 0.09 and 0.12) were synthesized by solid state reaction technique. The samples have been characterized by X-ray diffraction for structural and charge density analysis. XRD data show that the grown samples are orthorhombic in structure with single phase. The spatial charge density distribution in the unit cell for the synthesized samples has been studied using maximum entropy method. Further, the samples were analyzed by UV–visible spectrometry for optical properties and scanning electron microscopy for surface morphology. From the optical data, it was found that the direct band gap of the samples range from 2.27 to 2.46eV. The samples were also investigated by vibrating sample magnetometry for magnetic properties. From VSM data, it is inferred that all the samples in this series are found to be predominantly antiferromagnetic in nature. Since the doped lanthanum chromites have good mechanical properties and electrical conductivity at high temperature, these materials are used in solid oxide fuel cells (SOFC).

The helical surface states of the S-covered topological insulator Sb2Te3(0001)

The effects of S atom surface adsorption and substitution on the helical surface states of Sb2Te3 are studied by the density-functional theory with spin–orbit coupling being taken into account self-consistently. It is found that S atoms play the role of surface passivation when adsorbed on both surfaces of a 6QL Sb2Te3 film in symmetrical configuration. For symmetrical surfaces with both the top and bottom surfaces of a thin film with adsorbed S atoms, the linear dispersion of the surface states is found to be preserved and the topological surface states survive. The spatial distribution of charge density of the surface state at the point is also symmetric. For a film with asymmetric S atom adsorption, i.e., only one of the surfaces has adsorbed S atoms, the surface band structure is found to be very different. The degeneracy of the surface states from the two sides of a film is broken. The gap opens slightly at and the spatial distribution of charge density of the surface state at the point is also modified greatly. The Fermi level is robust against S impurity adsorption on the surface of Sb2Te3. Compared with S substitution, the effect of single surface S adsorption on electron structures is more prominent. This supports the idea that the topological insulator surface electronic states are dominated by its structural symmetry and the effect of the asymmetric environment of topological insulator Sb2Te3 films should thus be considered.

DFT-D Studies of Single Porphyrin Molecule on Doped Boron Silicon Surfaces

We present a theoretical study in the framework of density functional calculations, taking into account the van der Waals interactions (DFT-D) of isolated Cu-5,10,15,20-tetrakis(3,5-di-tert-butyl-phenyl) porphyrin (Cu-TBPP) molecules in a C2v conformation adsorbed on a Si(111)√3x√3R30°-boron surface [denoted Si(111)-B]. With this approach, we investigate interactions between perfect or boron-defect Si(111)-B substrates and the Cu-TBPP molecule as well as the consequences of demetallation of Cu-TBPP. For each model, we determine the structural equilibrium, the spatial charge-density distribution and the electronic properties of the ground state. We conclude that there is potential for Si adatom capture by a porphyrin without strong modification of the porphyrin response, as seen from simulated scanning tunneling microscopy (STM) images.

Computational strategies for 3D computation of the electric field in a vibratory tribocharger for mixed granular solids

In a previous paper, the authors introduced an original model for the computation of the triboelectric charges due to particle-to-particle collisions in a vibrated bed. The evaluation of the electric field inside the particle bed is a prerequisite for the accurate modelling of the tribochaging process, as it determines the trajectory of the particles as well as the charge swapping during collision. Two different approaches are presented and compared in terms of accuracy and computational time consumption. One consisted of computing the electric field as the superposition of the contributions of each point charge. The other, which proved to be much more effective, implied solving the Poisson equation for the potential generated by a given spatial distribution of charge density.

Electronic structure of twinned ZnS nanowires

The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs.

Elementary energy bands concept, band structure, and peculiarities of bonding in β-InSe crystal

The elementary energy bands concept together with the analysis of the Davydov-like splitting were applied for the first time for investigation of energy band structure and spatial electron density distribution in hexagonal crystals. This approach was used for consideration of the valence band states and for determination of peculiarities of the spatial charge density distribution in the unit cell of the layered β-InSe crystal. It was established that the valence charge density can be located in the so-called Van-der-Waals space. Conclusions following from the elementary energy bands concept were confirmed by the ab initio calculations of the band structure of β-InSe.

First-principles study of binary special quasirandom structures for the Al–Cu, Al–Si, Cu–Si, and Mg–Si systems

Based on special quasirandom structures (SQS’s) and first-principles calculations, enthalpies of mixing have been predicted for four binary fcc solid solutions in the Al–Cu, Al–Si, Cu–Si, and Mg–Si systems at nine compositions ( x = 0.0625 , 0.125, 0.1875, 0.25, 0.5, 0.75, 0.8125, 0.875, 0.9375, where x is the mole fraction of A atoms in the A–B binary system). The present results are compared with previous first-principles calculations and thermodynamic modeling results available in the literature. In order to provide insight into the understanding of mixing behavior for these solid solutions, the spatial charge density distributions in these binary solid solutions are also analyzed. The results obtained herein indicate that the SQS model can be used to estimate the thermodynamic properties of solid solutions, especially for metastable phases, the thermodynamic qualities of which are rarely measured.

Identification of the electroelastic coupling from full multi-physical fields measured at the micrometre scale

Metal coated microcantilevers are used as transducers of their electrochemical environment. Using the metallic layer of these cantilevers as a working electrode allows one to modify the electrochemical state of the cantilever surface. Since the mechanical behaviour of micrometre scale objects is significantly surface-driven, this environment modification induces bending of the cantilever. Using a full-field interferometric measurement set-up to monitor the objects then provides an optical phase map, which is found to originate from both electrochemical and mechanical effects. The scaling of the electrochemically-induced phase with respect to the surface charge density is modelled according to Gouy–Chapman–Stern theory, whereas the relationship between the mechanical effect and the surface charge density is analysed. An identification technique is described to determine a modelling of the electroelastic coupling and to identify the spatial charge density distribution from full-field phase measurements. Minimizing the least-squares gap between the measured phase and a statically admissible phase field, the mechanical effect is found to be charge-driven. The charge density field is also found to be singular on the cantilever edge, and the shear stress versus charge density is found to be non-linear.

Density-functional calculations of defect formation energies using supercell methods: Defects in diamond

Density-functional theory combined with periodic boundary conditions is used to systematically study the dependence of defect formation energy on supercell size for diamond containing vacancy and self-interstitial defects. We investigate the effect of the electrostatic energy due to the neutralization of charged supercells and the effect of the alignment of the valence band maximum (VBM) on the formation energy. For negatively charged vacancies and positively charged interstitials, the formation energies show a clear dependence on supercell size, and the electrostatic corrections agree with the trend given by the Makov-Payne scheme (Ref. 28). For positively charged vacancies and negatively charged interstitials, the size dependence and the electrostatic corrections are quite weak. An analysis of the spatial charge density distributions reveals that these large variations in electrostatic terms with defect type originate from differences in the screening of the defect-localized charge, as explained by using a simple electron-gas model. Several VBM alignment schemes are also tested. The best agreement between the calculated and asymptotically exact ionization levels is obtained when the levels are based on the formation energies referenced to the VBM of the defect-containing supercell.

Neural mesh iteration for the FE computation of charged-particle trajectories in vacuum electron devices

In this paper, a neural mesh-adaptation iterative procedure is presented for the finite-element solution of coupled steady-state electromechanical problems describing the motion of charged particles inside vacuum electron devices. In the procedure at each step a neural algorithm performs a mesh refinement in which the mesh "density" is related to the current estimate of the three-dimensional (3-D) spatial charge density distribution. Convergence to an accurate solution is obtained with a reduced computational effort in comparison with conventional fixed mesh iterative techniques. An example of application to the 3-D calculation of electron trajectories inside the collector of a travelling wave tube is shown in order to illustrate the advantages of the iterative scheme.