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Pure and M-doped (M=Zn, Cu, Ni, Co) cadmium oxide nanosheets, novel adsorbents for the adsorption of ethyl benzene and ortho, meta, para xylene: a theoretical study
摘要： The electronic and structural properties investigation of pure and zinc, copper, nickel, cobalt doped cadmium oxide nanosheets (CdONS) and the adsorption of ethyl benzene (EB) and ortho- meta- para xylene (OX, MX, PX) on these nanosheets were studied by density functional theory calculations. The adsorption energy, charge transfer, energy gap, spatial distribution of HOMO and LUMO orbitals and electron density scheme of ethyl benzene and ortho, meta, para xylene molecules on pure and doped CdONS are calculated. The obtained results show that the adsorption energy value increases after doping Zn, Cu, Ni and Co atoms in oxygen substituted state, especially in NiOCdONS and CoOCdONS. The adsorption energy of EB, OX, MX and PX on NiOCdONS and CoOCdONS is about ? 260?kJ/mol whereas its value on pure CdONS is approximately ? 100?kJ/mol. In comparison with pure CdONS, the adsorption energy of the molecules on MCdCdONS, decreases except in NiCdCdONS. The adsorption energy of OX, MX and PX on NiCdCdONS is ? 263.12, ? 150.94 and ? 151.85?kJ/mol, respectively. Also, the results show that the value of energy gap increases after the adsorption of EB, OX, MX and PX on CoOCdONS, therefore, CoOCdONS can be proposed as proper adsorbent and sensor for these molecules.
关键词： Adsorption,Ethyl benzene,Xylene,Cadmium oxide nanosheet,Density functional theory
更新于2025-09-10 09:29:36
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Structural, Optical and Magnetic Properties of Ultramarine Pigments: A DFT Insight
摘要： The ultramarine pigments are among the most widely used coloring materials since the antiquity till present times. Despite many experimental studies, the characterization of ultramarines is still incomplete. In this work we reported for the first time the density functional theory results obtained for realistic periodic and large cluster models of ultramarines with blue S3- and yellow S2- chromophores. Periodic calculations provided insight into Sn- siting inside aluminosilicate cages, normally not resolved well in experimental structural data. All electron calculations performed on large cluster models showed that the optical properties of S3- ions depend little on their orientation within cavities, unless strong distortion from free S3- ion C2v symmetry is enforced by the lattice. No magnetic coupling between S3- species occupying adjacent cages was found. Upon the present results observed differences in the averaging of electron resonance signals should be rather ascribed to different S3- dynamical effects. Though the quantitative computational treatment of S2- systems is more challenging, due to near orbital degeneracy, the qualitative results show that the electronic structure and spectroscopic properties of embedded S2- radicals are more sensitive to the environment than in the case of S3- species.
关键词： S3- chromophores,density functional theory,S2- chromophores,magnetic properties,aluminosilicate cages,ultramarine pigments,optical properties
更新于2025-09-10 09:29:36
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Unraveling the Structural and Electronic Properties of Graphene/Ge(110)
摘要： The direct growth of graphene on a semiconducting substrate opens a new avenue for future graphene-based applications. Understanding the structural and electronic properties of the graphene on a semiconducting surface is key for realizing such structures; however, these properties are poorly understood thus far. Here, we provide an insight into the structural and electronic properties of graphene grown directly on a Ge(110) substrate. Our scanning tunneling microscopy (STM) study reveals that overlaying graphene on Ge(110) promotes the formation of a new Ge surface reconstruction, i.e., a (6 × 2) superstructure, which has been never observed for a bare Ge(110) surface. The electronic properties of the system exhibit the characteristics of both graphene and Ge. The differential conductance (dI/dV) spectrum from a scanning tunneling spectroscopy (STS) study bears a parabolic structure, corresponding to a reduction in the graphene Fermi velocity, with exhibiting additional peaks stemming from the p-orbitals of Ge. The density functional theory (DFT) calculations confirm the existence of surface states due to the p-orbitals of Ge.
关键词： density functional theory calculations,scanning tunneling microscopy,Ge(110),scanning tunneling spectroscopy,Graphene,Ge surface reconstruction
更新于2025-09-10 09:29:36
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Hydrogenation and Fluorination of 2D Boron Phosphide and Boron Arsenide: A Density Functional Theory Investigation
摘要： First-principles density functional theory calculations are performed to study the stability and electronic properties of hydrogenated and fluorinated two-dimensional sp3 boron phosphide (BP) and boron arsenide (BAs). As expected, the phonon dispersion spectrum and phonon density of states of hydrogenated and fluorinated BX (X = P, As) systems are found to be different, which can be attributed to the different masses of hydrogen and fluorine. Hydrogenated BX systems bear larger and indirect band gaps and are found to be different from fluorinated BX systems. These derivatives can be utilized in hydrogen storage applications and ultrafast electronic devices. Finally, we investigated the stability and electronic properties of stacked bilayers of functionalized BP. Interestingly, we found that these systems display strong interlayer interactions, which impart strong stability. In contrast with the electronic properties determined for the fluorinated/hydrogenated monolayers, we found that the electronic properties of these bilayers can finely be tuned to a narrow gap semiconductor, metallic or nearly semimetallic one by selecting a suitable arrangement of layers. Moreover, the nearly linear dispersion of the conduction band edge and the heavy-, light-hole bands are the interesting characteristics. Furthermore, the exceptional values of effective masses assure the fast electronic transport, making this material very attractive to construct electronic devices.
关键词： boron phosphide,boron arsenide,hydrogenation,fluorination,density functional theory,electronic properties,stability
更新于2025-09-10 09:29:36
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In situ Raman spectroscopic evidence for oxygen reduction reaction intermediates at platinum single-crystal surfaces
摘要： Developing an understanding of structure–activity relationships and reaction mechanisms of catalytic processes is critical to the successful design of highly efficient catalysts. As a fundamental reaction in fuel cells, elucidation of the oxygen reduction reaction (ORR) mechanism at Pt(hkl) surfaces has remained a significant challenge for researchers. Here, we employ in situ electrochemical surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) calculation techniques to examine the ORR process at Pt(hkl) surfaces. Direct spectroscopic evidence for ORR intermediates indicates that, under acidic conditions, the pathway of ORR at Pt(111) occurs through the formation of HO2*, whereas at Pt(110) and Pt(100) it occurs via the generation of OH*. However, we propose that the pathway of the ORR under alkaline conditions at Pt(hkl) surfaces mainly occurs through the formation of O2?. Notably, these results demonstrate that the SERS technique offers an effective and reliable way for real-time investigation of catalytic processes at atomically flat surfaces not normally amenable to study with Raman spectroscopy.
关键词： density functional theory,in situ Raman spectroscopy,electrochemical surface-enhanced Raman spectroscopy,oxygen reduction reaction,platinum single-crystal surfaces
更新于2025-09-10 09:29:36
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Resolution-of-identity accelerated relativistic two- and four-component electron dynamics approach to chiroptical spectroscopies
摘要： We present an implementation and application of electron dynamics based on real-time time-dependent density functional theory (RT-TDDFT) and relativistic 2-component X2C and 4-component Dirac–Coulomb (4c) Hamiltonians to the calculation of electron circular dichroism and optical rotatory dispersion spectra. In addition, the resolution-of-identity approximation for the Coulomb term (RI-J) is introduced into RT-TDDFT and formulated entirely in terms of complex quaternion algebra. The proposed methodology was assessed on the dimethylchalcogenirane series, C4H8X (X = O, S, Se, Te, Po, Lv), and the spectra obtained by non-relativistic and relativistic methods start to disagree for Se and Te, while dramatic differences are observed for Po and Lv. The X2C approach, even in its simplest one-particle form, reproduces the reference 4c results surprisingly well across the entire series while offering an 8-fold speed-up of the simulations. An overall acceleration of RT-TDDFT by means of X2C and RI-J increases with system size and approaches a factor of almost 25 when compared to the full 4c treatment, without compromising the accuracy of the final spectra. These results suggest that one-particle X2C electron dynamics with RI-J acceleration is an attractive method for the calculation of chiroptical spectra in the valence region.
关键词： resolution-of-identity approximation,complex quaternion algebra,chiroptical spectroscopies,real-time time-dependent density functional theory,relativistic Hamiltonians,electron dynamics
更新于2025-09-10 09:29:36
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FIRST PRINCIPLES STUDY OF STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF HALF-HEUSLER ALLOYS LIMGN, NaMGN AND KMGN
摘要： In this study, we performed our calculations using the full-potential linearized-augmented plane wave (FP-LAPW) method as implemented in the WIEN2k code based on DFT. The generalized gradient functional with the Wu-Cohen (WC) parameterization was used to evaluate the structural, electronic, optical and thermoelectric properties of the materials under this study. We have calculated the structural parameters and our obtained results are in good agreement with available experimental and previous theory calculations. The density of states and band structure figures have been calculated and analyzed. The optical properties that covered by dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and energy-loss function have been calculated and analyzed in a range energy from 0eV to 30eV.
关键词： generalized gradient functional,dielectric function,reflectivity,absorption,half-Heusler,Density functional theory
更新于2025-09-09 09:28:46
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The Nature of the Oxygen Vacancy in Amorphous Oxide Semiconductors: Shallow Versus Deep
摘要： Using first-principles calculation, we investigate the nature of oxygen vacancy (VO), namely shallow versus deep, in the amorphous oxide semiconductor InGaZnO4 (a-IGZO), which has not been fully clarified despite its technological importance. Oxygen-deficient amorphous models are generated through the hybrid functional molecular dynamics (MD) simulations that allow for finding stable VO configurations while minimizing computational approximations. From eight independent models, we consistently find that VO serves as the shallow donor, increasing the Fermi level above the conduction band minimum. For comparison purpose, we also generate deep VO models by charging the system during MD simulations. It is found that deep VO is higher in the formation energy than shallow VO, confirming that shallow VO is the preferred type of oxygen vacancies in a-IGZO.
关键词： hybrid functional,computational physics,InGaZnO4,oxygen vacancy,density functional theory
更新于2025-09-09 09:28:46
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Electronic structures of impurities and point defects in semiconductors
摘要： A brief history of the impurity theories in semiconductors is provided. A bound exciton model is proposed for both donor- and acceptor-like impurities and point defects, which offers a uni?ed understanding for “shallow” and “deep” impurities and point defects. The underlying physics of computational results using different density-functional theory-based approaches are discussed and interpreted in the framework of the bound exciton model.
关键词： hydrogen model,effective-mass theory,bound exciton,deep impurity,density-functional theory,shallow impurity,semiconductor
更新于2025-09-09 09:28:46
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Radially resolved electronic structure and charge carrier transport in silicon nanowires
摘要： The electronic structure of silicon nanowires is studied using density functional theory. A radially resolved density of states is discussed for different nanowire diameters and crystal orientations. This approach allows the investigation of spatially varying electronic properties in the radial direction and extends previous studies, which are usually driven by a one-dimensional band structure analysis. We demonstrate strong differences in the electronic structure between the surface and the center of the nanowire, indicating that the carrier transport will mainly take place in the center. For increasing diameters, the density of states in the center approaches the bulk density of states. We find that bulk properties, such as the indirect nature of the band gap, become significant at a nanowire diameter of approximately 5 nm and beyond. Finally, the spatial characteristic of the current is visualized in terms of transmission pathways on the atomic scale. Electron transport is found to be more localized in the nanowire center than the hole transport. It also depends on the crystal orientation of the wire. For the growing demand of silicon nanowires, for example in the field of sensors or field-effect transistors, multiple conclusions can be drawn from the present work, which we discuss towards the end of the publication.
关键词： charge carrier transport,radially resolved density of states,silicon nanowires,density functional theory,electronic structure
更新于2025-09-09 09:28:46