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Energetics and electronic structures of polymeric all-benzene hollow-cages and planar networks
摘要： We studied the energetics and electronic structure of polymerized benzene hollow-cages and sheet using the density functional theory with the generalized gradient approximation. The energetics and electronic structure of the polymeric benzene cages and sheet depend on their size and dimensionality. Because of the symmetric network topology as well as the constituent benzene units, the cages possess highly bunched states around the Fermi level. The energy gap between the highest occupied and the lowest unoccupied states of the cages is approximately proportional to their curvature, owing to the decrease of the strain. The polymerized benzene sheet is a direct gap semiconductor with the gap of 2.4 eV between the less dispersive states of the highest branch of the valence and the lowest branch of the conduction bands.
关键词： density functional theory,electronic structure,planar networks,polymerized benzene,hollow-cages
更新于2025-09-10 09:29:36
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Atomic Structure and Electrical Activity of Grain Boundaries and Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite
摘要： To evaluate the role of planar defects in lead-halide perovskites—cheap, versatile semiconducting materials—it is critical to examine their structure, including defects, at the atomic scale and develop a detailed understanding of their impact on electronic properties. In this study, postsynthesis nanocrystal fusion, aberration-corrected scanning transmission electron microscopy, and first-principles calculations are combined to study the nature of different planar defects formed in CsPbBr3 nanocrystals. Two types of prevalent planar defects from atomic resolution imaging are observed: previously unreported Br-rich [001](210)∑5 grain boundaries (GBs) and Ruddlesden–Popper (RP) planar faults. The first-principles calculations reveal that neither of these planar faults induce deep defect levels, but their Br-deficient counterparts do. It is found that the ∑5 GB repels electrons and attracts holes, similar to an n–p–n junction, and the RP planar defects repel both electrons and holes, similar to a semiconductor–insulator–semiconductor junction. Finally, the potential applications of these findings and their implications to understand the planar defects in organic–inorganic lead-halide perovskites that have led to solar cells with extremely high photoconversion efficiencies are discussed.
关键词： Ruddlesden–Popper faults,lead-halide perovskites,scanning transmission electron microscopy,density-functional theory,grain boundaries
更新于2025-09-10 09:29:36
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Effect of multiorbital contributions to strong-field ionization of benzene derivatives
摘要： Strong-?eld ionization of benzene, ?uorobenzene, benzonitrile, and 1-chloro-2-?uorobenzene is studied within the framework of real-space and real-time time-dependent density functional theory. Analysis of the ionization rates as a function of the molecule orientation reveals a signi?cant contribution from multiple inner Kohn-Sham orbitals that depends on the electronic structure and on the orbital symmetries of the molecule, as well as on the polarization and intensity of the external laser ?eld. Calculated photoelectron angular distributions at different molecular orientations and in response to laser ?elds with different degrees of ellipticity further demonstrate the spatial dependency of the orbital ionization rates.
关键词： orbital symmetries,time-dependent density functional theory,strong-?eld ionization,benzene derivatives,photoelectron angular distributions
更新于2025-09-10 09:29:36
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Complex band structure calculations based on the overbridging boundary matching method without using Green's functions
摘要： A complex band structure describes the dispersion relation not only of propagating bulk states but also of evanescent ones, both of which are together referred to as generalized Bloch states and are important for understanding the electronic nature of solid surfaces and interfaces. On the basis of the real-space finite-difference formalism within the framework of the density functional theory, we formulate the Kohn-Sham equation for generalized Bloch wave functions as a generalized eigenvalue problem without using any Green’s function matrix. By exploiting the sparseness of the coefficient matrices and using the Sakurai-Sugiura projection method, we efficiently solve the derived eigenvalue problem for the propagating and slowly decaying/growing evanescent waves, which are essential for describing the physics of surface/interface states. The accuracy of the generalized Bloch states and the computational efficiency of the present method in solving the eigenvalue problem obtained are compared with those by other methods using the Green’s function matrix. In addition, we propose two computational techniques to be combined with the Sakurai-Sugiura projection method and achieve further improvement in the accuracy and efficiency. Complex band structures are calculated with the present method for single- and multiwall carbon nanotubes, and the interwall hybridization and branch points of evanescent electronic states observed in the imaginary parts of the band structures are also discussed.
关键词： Sakurai-Sugiura projection method,density functional theory,generalized Bloch states,carbon nanotubes,complex band structure
更新于2025-09-10 09:29:36
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Water Dissociation and Hydroxyl Ordering on Anatase
摘要： We studied the interaction of water with the anatase TiO2e001T surface by means of scanning tunneling microscopy, x-ray photoelectron spectroscopy, and density functional theory calculations. Water adsorbs dissociatively on the ridges of a (1 × 4) reconstructed surface, resulting in a (3 × 4) periodic structure of hydroxyl pairs. We observed this process at 120 K, and the created hydroxyls desorb from the surface by recombination to water, which occurs below 300 K. Our calculations reveal the water dissociation mechanism and uncover a very pronounced dependence on the coverage. This strong coverage dependence is explained through water-induced reconstruction on anatase TiO2e001T-e1 × 4T. The high intrinsic reactivity of the anatase TiO2e001T surface towards water observed here is fundamentally different from that seen on other surfaces of titania and may explain its high catalytic activity in heterogeneous catalysis and photocatalysis.
关键词： x-ray photoelectron spectroscopy,scanning tunneling microscopy,anatase TiO2,hydroxyl ordering,density functional theory,water dissociation
更新于2025-09-10 09:29:36
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Formation energies of CdSe wurtzoid and diamondoid clusters formed from Cd and Se atomic clusters
摘要： Cadmium Selenide thermodynamic formation energies at the molecular and nanoscale range are investigated using density functional theory. The investigation is performed using wurtzoid and diamondoid clusters that represent the wurtzite and zincblende structures at the molecular and nanoscale size range for a cluster number of atoms n ≤ 26. Cd and Se atomic clusters are optimized and used to provide component atomic cluster energies. Although both Cd and Se clusters at the nanoscale have di?erent phases than bulk, the results show that Gibbs free energy, enthalpy, and entropy of formation of CdSe are close to their experimental bulk energies of formation within errors of experimental measurements. CdSe wurtzoids generally have higher absolute (more negative) Gibbs free energy of formation than CdSe diamondoids indicating more stable wurtzoid molecules which is also the case at bulk. The absolute Gibbs free energy of wurtzoids is also higher than experimental value (more negative) because of surface e?ects at the nanoscale. Enthalpy of formation indicates an exothermic reaction of Cd and Se clusters as is the case at bulk. The entropy of formation of all clusters is size-sensitive and converges towards bulk experimental measurements. Both wurtzoids and diamondoids members contain Cd13Se13 cluster which is the most investigated magic CdSe cluster.
关键词： Density functional theory,CdSe,Cluster
更新于2025-09-10 09:29:36
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Width dependent structural and electrical properties of zigzag ZnTe nanoribbons
摘要： We carry out density functional theory based investigation to understand the structural and electrical properties such as atomic structure, edge energy, band gap, and work function of zigzag ZnTe nanoribbons. It is found that the zigzag nanoribbons may be stabilized by passivating the edge atoms with Hydrogen, Oxygen or Fluorine atoms. Our study reflects that zigzag ZnTe nanoribbons with smaller width behave like semiconductor. However, they exhibit a transition from semiconducting phase to a metallic phase as width increases. A wide variation of band gap is obtained with respect to the choice of edge passivating elements. Work functions of all the nanoribbons are also estimated in order to assess the utility of these nanoribbons in various field emission devices.
关键词： Density functional theory,Work function,Band gap,Nanoribbon
更新于2025-09-10 09:29:36
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Probing Basis Set Requirements for Calculating Core Ionization and Core Excitation Spectroscopy by the ΔSCF Approach
摘要： We investigate the basis set requirements for calculating properties corresponding to removing core electrons by the ΔSCF approach using Hartree-Fock and density functional theory. Standard contracted basis sets are shown to produce large errors and the improved performance of core-augmented basis sets is traced to the fact that the core-augmenting functions effectively creates an auxiliary set of uncontracted function in the core region. We propose two specific basis sets of double and triple zeta quality based on exponent interpolation of the polarization consistent basis sets, denoted pcX-1 and pcX-2, that display significantly lower basis set errors compared to other alternatives. These are suitable for both non-relativistic and relativistic calculations of the Douglas-Kroll-Hess type, with typical basis set errors of 0.1 and 0.01 eV, respectively, and they can be used in a mixed basis set approach with only a minor degradation in performance. The versions augmented with diffuse functions (aug-pcX-1 and aug-pcX-2) are shown to perform better than other alternatives for X-ray absorption spectroscopy. When used in connection with range-separated hybrid density functional methods and relativistic corrections, the pcX-n basis sets can in favorable cases reproduce experimental results to within a few tenths of an eV.
关键词： basis sets,Hartree-Fock,density functional theory,ΔSCF approach,core ionization,core excitation spectroscopy
更新于2025-09-10 09:29:36
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Electronic exchange-correlation, many-body effect issues on first-principles calculations of bulk SiC polytypes
摘要： The first-principles Projector-Augmented Wave method (PAW) is used to investigate the electronic, phonon band structure and dielectric properties of four bulk silicon carbide (SiC) polytypes. We employ PAW pseudopotential density functional theory with Perdew, Burke and Ernzerhof (PBE) and hybrid HSE06 approximations of the exchange-correlation functional. Many-body effects are incorporated using the GW approximation of the self-interaction to study SiC properties. GW method in its single-shot variant, which is based on the many-body perturbation theory (MBPT), is used to calculate the quasi-particle (QP) energies of the band structure and the dielectric properties for different polytypes. The electronic band structure determination within GW method uses the Wannier procedure where a basis set of maximally localized Wannier function (MLWF) is constructed to interpolate the QP energies of few regular mesh k-points to the high-symmetry lines in Brillouin zone. As a consequence of QP correction to the Kohn–Sham energies, bandgap is increased by upto 3 eV in case of 4H–SiC, as compared to PBE bandgap. GW results are comparable to those of hybrid functionals and are in good agreement with the experimental results. The optical properties are then studied within PBE, HSE06 and include many-body effects. In addition, the phonon band structure has been investigated within HSE06 and compared to previous PBE results. We found good agreement with the previous theoretical results and the experimental available data.
关键词： silicon carbide,semiconductors,Density functional theory,power electronic device,polytypism
更新于2025-09-10 09:29:36
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Strategies to facilitate the formation of free standing MoS <sub/>2</sub> nanolayers on SiO <sub/>2</sub> surface by atomic layer deposition: A DFT study
摘要： In this study, we employ density functional theory calculations to investigate the very initial formation of a buffer layer during atomic layer deposition of MoS2 at the SiO2 (001) surface. In our previous study, we described that the self-limiting atomic layer deposition (ALD) reactions using Mo(NMe2)2(NtBu)2 as precursor and H2S as co-reagent terminate in the formation of a so-called building block on the SiO2 (001) surface. This building block consists of Mo which shares bonds with the surface O of SiO2 (001) at the bottom and terminal S at the top. Electronic band structure calculations indicate that the subsequently deposited buffer-layer that is composed of these building blocks has (opto)-electrical properties that are far from the ideal situation. Based on our studies, we propose alternative ALD chemistries which lead to the formation of a so-called underpinned building block. In this cluster, the Mo atoms are underpinned by S atoms, suppressing the formation of a buffer layer. This ultimately facilitates the formation of a free standing conformal 2D-MoS2 nanolayer at the interface. Through the proposed chemistries, the opto-electrical properties of the deposited layers will be preserved.
关键词： opto-electrical properties,MoS2,SiO2,density functional theory,atomic layer deposition
更新于2025-09-10 09:29:36