- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
The model of the fullerene C60 and its ions C60+, C60??pseudopotentials for molecular dynamics purposes
摘要： The model pseudopotentials of C?60, C60 and C+60 have been constructed on the base of the total electrostatic potentials obtained as a result of ab initio-based calculations. The radial distance dependence of the pseudopotential is obtained by averaging with respect to the spherical angles of the total electrostatic potential. The role of the electronic correlations is investigated by comparison results of using of the di?erent exchange-correlation functional within the density functional theory. All pseudopotentials are ?tted by the ?ne approximation functions and can be applied for molecular dynamics tasks.
关键词： molecular dynamics,electronic correlations,pseudopotentials,fullerene C60,ab initio calculations
更新于2025-09-10 09:29:36
-
Design Principles for Trap-Free CsPbX <sub/>3</sub> Nanocrystals: Enumerating and Eliminating Surface Halide Vacancies with Softer Lewis Bases
摘要： We introduce a general surface passivation mechanism for cesium lead halide perovskite materials (CsPbX3, X = Cl, Br, I) that is supported by a combined experimental and theoretical study of the nanocrystal surface chemistry. A variety of spectroscopic methods are employed together with ab initio calculations to identify surface halide vacancies as the predominant source of charge trapping. The number of surface traps per nanocrystal is quantified by 1H NMR spectroscopy, and that number is consistent with a simple trapping model in which surface halide vacancies create deleterious under-coordinated lead atoms. These halide vacancies exhibit trapping behavior that differs between CsPbCl3, CsPbBr3, and CsPbI3. Ab initio calculations suggest that introduction of anionic X-type ligands can produce trap-free band gaps by altering the energetics of lead-based defect levels. General rules for selecting effective passivating ligand pairs are introduced by considering established principles of coordination chemistry. Introducing softer, anionic, X-type Lewis bases that target under-coordinated lead atoms results in absolute quantum yields approaching unity and monoexponential luminescence decay kinetics, thereby indicating full trap passivation. This work provides a systematic framework for preparing highly luminescent CsPbX3 nanocrystals with variable compositions and dimensionalities, thereby improving fundamental understanding of these materials and informing future synthetic and post-synthetic efforts towards trap-free CsPbX3 nanocrystals.
关键词： charge trapping,nanocrystals,surface passivation,ab initio calculations,halide vacancies,CsPbX3,ligand exchange,quantum yield
更新于2025-09-10 09:29:36
-
Pb phases on Si(111)
摘要： We present here a combined experimental Raman spectroscopy and ab initio theoretical study of the (√3×√3) reconstructed SIC phase of Pb on Si(111) and discuss their relation to the atomic surface structure. The Raman response of the surface localized vibrational modes, in particular, is identified in the low-frequency spectral range (down to 15 cm?1). We demonstrate that Raman spectroscopy is a very powerful approach to test atomic structures of surfaces and a valuable complement to standard surface analytics. While the calculated spectra of H3 and T4 are too similar to allow a discrimination of these phases, the good overall agreement to the measured Raman spectra enables a classification of the observed vibrational modes.
关键词： surface vibrations,Pb/Si(111),atomic structure,ab initio,Raman spectroscopy
更新于2025-09-10 09:29:36
-
Structural evolution of oxygen on the surface of TiAlN: Ab initio molecular dynamics simulations
摘要： We have employed ab initio molecular dynamics simulations to study the oxidation behavior of TiAlN hard coatings as a function of Al content and temperature. Results show that for TiAlN with a low Al content (Ti0.75Al0.25N), Ti atoms can always bond with O atoms, while Al atoms bond with O only at a higher temperature. For Ti0.5Al0.5N, both Al and Ti can bond with O atoms, irrespective of temperature. Through analyzing the displacement height of O-bonded metal atoms, we suggest that titanium oxide nucleates at the outermost layer of Ti0.75Al0.25N while the outermost layer after Ti0.5Al0.5N is exposed to oxygen is aluminum oxide. Our simulation results predict, in agreement with experiment, that Ti0.5Al0.5N has superior oxidation resistance in comparison with Ti0.75Al0.25N. This study provides an atomistic insight to the initial stage of the oxidation process, which is else di?cult to observe experimentally.
关键词： Oxidation,TiAlN,Hard coating,Ab initio molecular dynamics
更新于2025-09-10 09:29:36
-
Frequency dependent linear and nonlinear optical properties of compositionally tuned inorganic CsSnX (X = Br, I) composites
摘要： Structural, electronic and optical properties of CsSnX (X = Br, I) system have been thoroughly investigated by means of an unbiased crystal structure screening, density functional theory and perturbation approach. Crystallography of known parent structures, CsI and CsBr were well replicated compared to experimental observations. Experimentally verified cubic Cs2SnI6 phase was operatively reproduced. Its computed crystal class and simulated XRD pattern match the available experimental data, hence signifying the robustness of methodology applied. Other energetically and dynamically stable structures include cubic Cs2SnBr6, triclinic Cs2Sn2Br6 and Cs2Sn2I6. These phases are direct semiconductors which exhibit non-monotonic association between GW corrected band gap and halogen type or atomic mass. Instead, their energy gap is determined by the structure of CsSn halide compounds, and span an energy range from mid infrared to near ultraviolet region. The GW-raised gap was incorporated as scissor shift to ensure good reliability of optical calculations. Dynamical dielectric function, adsorption coefficient, energy-loss and refractive index spectrum of aforementioned phases were acquired. Both novel Cs2Sn2Br6 and Cs2Sn2I6 phases have impressive zero limit second-order susceptibility ranging from 3.1 pm V-1 to 22.8 pm V-1.
关键词： Ab initio,Optical Properties,Stable phases,Density functional theory
更新于2025-09-10 09:29:36
-
Dopants Control of Electron-Hole Recombination in Cesium-Titanium Halide Double Perovskite by Time Domain Ab Initio Simulation: Co-Doping Supersedes Mono-Doping
摘要： Using nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory, we simulate electron-hole recombination in pristine and doped inorganic Pb-free double perovskite Cs2TiBr6. We show that replacing the titanium and/or bromine with silicon and/or chlorine extends the charge carrier lifetime. Importantly, dopants avoid deep traps despite they do not change the fundamental bandgap of Cs2TiBr6, they decrease the NA electron-phonon coupling and accelerate decoherence, arising from the reduced overlap of electron and hole wave functions as well as fast phonon modes induced by light dopants respectively, suppressing electron-hole recombination. More importantly, co-doping can reduce the formation energy of silicon and achieve higher doping concentration, potentially increasing the lifetime further. Our study suggests a rational strategy to reduce energy losses by co-doping in design of high performance all-inorganic Pb-free perovskite solar cells.
关键词： Co-doping,Electron-Hole Recombination,Mono-doping,Energy Conversion and Storage,Cesium-Titanium Halide Double Perovskite,Plasmonics and Optoelectronics,Time Domain Ab Initio Simulation,Dopants Control
更新于2025-09-10 09:29:36
-
First vibrational investigations of N <sub/>2</sub> O–H <sub/>2</sub> O, N <sub/>2</sub> O–(H <sub/>2</sub> O) <sub/>2</sub> , and (N <sub/>2</sub> O) <sub/>2</sub> –H <sub/>2</sub> O complexes from the far to the near-infrared spectral region by neon matrix isolation and <i>ab initio</i> calculations
摘要： We present for the first time the investigation of water molecules complexed with dinitrogen monoxide, two abundant molecules in atmosphere, in solid neon using Fourier transform infrared (IR) spectroscopy. We identify at least three complexes from concentration effects, N2O–H2O, N2O–(H2O)2, and (N2O)2–H2O, by observation of new absorption bands close to the monomer fundamental modes from the far to the near IR region. We highlight the presence of isomers for the N2O–H2O complex with the help of theoretical calculations at second order M?ller-Plesset (MP2) and coupled-cluster single double triple-F12a/aug-cc-pVTZ levels. The observed frequencies for the N2O–(H2O)2 and (N2O)2–H2O complexes are compared with MP2/aug-cc-pVTZ harmonic data. Anharmonic coupling constants have been derived from the observations of overtones and combination bands.
关键词： ab initio calculations,anharmonic coupling constants,neon matrix isolation,N2O–H2O complexes,Fourier transform infrared spectroscopy
更新于2025-09-09 09:28:46
-
Dipole Moment and Electronic Structure Calculations of the Electronic States of the Molecule SiC below 97000cm-1
摘要： Beside its importance in the astrophysics, the silicon carbide has a great importance in the industry of semiconductors and ceramics. Because of the absence of theoretical data, extensive ab initio calculations of dipole moment and higher excited electronic state have been done for this molecule. These calculations have been performed by using the Complete Active Space Self Consistent Field (CASSCF) with Multireference Configuration Interaction MRCI+Q (singly and doubly excitation with Davidson corrections). The potential energy and the dipole moment curves for the 47 low-lying singlet, triplet and quintet electronic states in the representation 2s+1Λ(+/-) of the molecule SiC have been calculated. The harmonic frequency ωe, the internuclear distance Re, the electronic energy with respect to the ground state Te, the rotational constants Be and the permanent dipole moment have been obtained for these electronic states. The comparison between the values of the present work and those available in the literature, for several electronic states, shows a good agreement. In the present work thirteen new electronic states have been investigated here for the first time. These new results may leads to more investigation of new experimental works on this molecule.
关键词： electronic structure,spectroscopic constants,permanent dipole moments,potential energy curves,ab initio calculation
更新于2025-09-09 09:28:46
-
-II
摘要： The basic and the charge density wave (CDW) structures of the monoclinic NbS3-II polymorph were studied by synchrotron x-ray diffraction, ab initio calculations, simulation of electron diffraction patterns, and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is con?rmed that the basic structure belongs to the space group P 21/m and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns [a0 = 0.96509(8) nm, b0 = 0.33459(2) nm, c0 = 1.9850(1) nm, and β0 = 110.695(4)?]. The incommensurate components of the two CDWs, (cid:3)q1 = (0, 0.298, 0) and (cid:3)q2 = (0, 0.352, 0), are related as q1b + 2q2b ≈ 1. Both CDWs form their own modulation patterns with unit cells (am = 2a0, bm = b0/qjb, cm = c0, βm = β0) and are ordered along adjacent isosceles TP columns either pairwise or with both columns modulated by either the (cid:3)q1 or (cid:3)q2 CDW only. The CDWs are ordered according to one of the two possible modulation pattern space groups, Cm or C2/m. If considered as long-period commensurate, the entire modulated structure with both CDWs included is described within experimental error with an enlarged unit cell (a = 2a0, b = 37b0, c = c0, and β = β0) and with all atoms displaced from their average positions in accord with the speci?ed modulation pattern.
关键词： synchrotron x-ray diffraction,ab initio calculations,charge density wave,scanning tunneling microscopy,transmission electron microscopy,NbS3-II
更新于2025-09-09 09:28:46
-
Silicide phase formation by Mg deposition on amorphous Si. Ab initio calculations, growth process and thermal stability
摘要： Formation of magnesium silicides on amorphous silicon by deposition of Mg at room temperature is studied by electron energy loss spectroscopy, differential reflectance spectroscopy and high resolution transmission electron microscopy. Optimal crystal structures of Mg silicides under high pressure are found by ab initio DFT calculations. These structures are related to the particular minima of enthalpy. Dielectric functions are calculated for these structures. The transitions from the cubic phase c-Mg2Si to orthorhombic o-Mg2Si at 5.6 GPa and then from o-Mg2Si to hexagonal h-Mg2Si at 22.3 GPa are predicted using the USPEX code. The experimental spectra and the data obtained from the calculated dielectric functions are mutually consistent. Optical reflectance is suitable for monitoring the growth and transformations of the phases during experiments. During Mg deposition onto amorphous Si, the o-Mg2Si phase forms first, then the c-Mg2Si phase grows upon it. The observed sequence of phase formation is related with the compression stress arising in the depth of the Mg-Si mixture.
关键词： optical reflection spectroscopy,electron energy loss spectroscopy,solid state reactions,thin films,high resolution transmission electron spectroscopy,ab initio calculations
更新于2025-09-09 09:28:46