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First-principles many-body study of the electronic and optical properties of CsK <sub/>2</sub> Sb, a semiconducting material for ultra-bright electron sources
摘要： We present a comprehensive first-principles investigation of the electronic and optical properties of CsK2Sb, a semiconducting material for ultra-bright electron sources for particle accelerators. Our study, based on density-functional theory and many-body perturbation theory, provides all the ingredients to model the emission of this material as a photocathode, including band gap, band dispersion, and optical absorption. An accurate description of these properties beyond the mean-field picture is relevant to take into account many-body effects. We discuss our results in the context of state-of-the-art electron sources for particle accelerators to set the stage towards improved modeling of quantum efficiency, intrinsic emittance, and other relevant quantities determining the macroscopic characteristics of photocathodes for ultra-bright beams.
关键词： theoretical spectroscopy,electronic structure,alkali antimonides,density-functional theory
更新于2025-09-09 09:28:46
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Exciting vibrons in both frontier orbitals of a single hydrocarbon molecule on graphene
摘要： Vibronic excitations in molecules are key to the fundamental understanding of the interaction between vibrational and electronic degrees of freedom. In order to probe the genuine vibronic properties of a molecule even after its adsorption on a surface appropriate bu?er layers are of paramount importance. Here, vibrational progression in both molecular frontier orbitals is observed with submolecular resolution on a graphene-covered metal surface using scanning tunnelling spectroscopy. Accompanying calculations demonstrate that the vibrational modes that cause the orbital replica in the progression share the same symmetry as the electronic states they couple to. In addition, the vibrational progression is more pronounced for separated molecules than for molecules embedded in molecular assemblies. The entire vibronic spectra of these molecular species are moreover rigidly shifted with respect to each other. This work unravels intramolecular changes in the vibronic and electronic structure owing to the e?cient reduction of the molecule–metal hybridization by graphene.
关键词： single molecules,quantum chemistry,density functional theory,vibrational progression,graphene,scanning tunnelling microscopy,frontier orbitals
更新于2025-09-09 09:28:46
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First principle analysis for magnetic properties of noble metal doped rutile TiO2
摘要： From first principle analysis, it is shown that non-magnetic TiO2 can be made magnetic using successive doping of Ag and Au at Ti-site. However, Pt-doped TiO2 remains magnetically inert. Effect of another defect in the form of oxygen vacancy adjacent to doped atom has also been carried out. To quantify effect of doping; magnetic moment, Gibbs free energy and defect formation energy has been calculated for each structure. Further, for both the dopants the spin-spin interaction studies reveal that the ferromagnetic (FM) spin ordered system is more stable than the anti ferromagnetic (AFM) one. These theoretical calculations will be used to choose proper ways of chemical synthesis for Ag and Au doped TiO2.
关键词： Magnetic semiconductors,Density-functional theory,Defects
更新于2025-09-09 09:28:46
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Engineering SrSnO <sub/>3</sub> Phases and Electron Mobility at Room Temperature Using Epitaxial Strain
摘要： High-speed electronics require epitaxial films with exceptionally high carrier mobility at room temperature. Alkaline-earth stannates with high room-temperature mobility show outstanding prospects for oxide electronics operating at ambient temperatures. However, despite significant progress over the last few years, mobility in stannate films has been limited by dislocations due to the inability to grow fully coherent films. Here, we demonstrate the growth of coherent, strain-engineered phases of epitaxial SrSnO3 (SSO) films using a radical-based molecular beam epitaxy approach. Compressive strain stabilized the high-symmetry tetragonal phase of SSO at room temperature (RT), which, in bulk, exists only at temperatures between 1062 K and 1295 K. We achieved a mobility enhancement of over 300% in doped films compared with the low temperature orthorhombic polymorph. Using comprehensive temperature-dependent synchrotron-based X-ray measurements, electronic transport and first principles calculations, crystal and electronic structures of SSO films were investigated as a function of strain. We argue that strain-engineered films of stannate will enable high mobility oxide electronics operating at RT with the added advantage of being optically transparent.
关键词： phase transition,Hybrid molecular beam epitaxy,half-order diffraction,strain engineering,density functional theory,high mobility,Octahedral rotations
更新于2025-09-09 09:28:46
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Graphene based nanocomposites for efficient photocatalytic hydrogen evolution: insight into the interface toward separation of photogenerated charges
摘要： Although the reduced graphene oxide (rGO) has been intensively applied to photocatalytic H2 evolution, no enough attention was given to study the interface between photocatalyst and rGO, which is the key point to affect the transportation of photogenerated electron. Herein, in order to research the heterojunctions interface, the series of SrTiO3 photocatalysts with different crystal facets were fabricated to load with rGO for photocatalytic H2 evolution. The characterization measurements and theory calculation verified that the rGO was mainly anchored on the Ti-O bond of SrTiO3. So, compared to {001} facets sample, the {110} facets of SrTiO3, exposed more Ti and O atoms, could form stronger bond with the rGO. Additionally, DFT study deduced that the photoinduced electron could immigrate rapidly from Ti-O bond to the rGO, which was in good agreement with the results of photoelectrochemical and photoluminescence (PL) experiments. Meanwhile, experimentally, the 1 % wt. rGO@SrTiO3 with {110} facets nanocomposite showed the superior photocatalytic H2 yield rate (3.82 mmol/h/g), which was 2.2 times and 3.2 times higher than that of pure SrTiO3 with the same facets and 1 % wt. rGO@SrTiO3 with {001} facets, respectively. Both experiments and theoretical calculations unveiled that the synergetic effect of SrTiO3 facets engineering and rGO loading effectively prompted the immigration of photoinduced electron at the nanocomposites interface. This work provides a rational thinking of a high efficiency rGO-based heterogeneous photocatalysts for solar energy conversion.
关键词： density functional theory study,rGO-based heterogeneous photocatalysts,separation of photogenerated charges,photocatalytic hydrogen evolution,SrTiO3,electron screening effect
更新于2025-09-09 09:28:46
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Bandgap opening in graphene using alkali ions by first principles
摘要： Recently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na+, K+, and Cs+ ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene.
关键词： bandgap opening,graphene,alkali ions,Stone-Wales defects,substitutional defects,Density Functional Theory,first principles
更新于2025-09-09 09:28:46
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Theoretical study of charge-transport and optical properties of indeno[1,2- <i>b</i> ]fluorene-6,12-dione-based semiconducting materials
摘要： The conducting and optical properties of a series of indeno[1,2-b]fluorene-6,12-dione (IFD)-based molecules have been systematically studied and the influences of butyl, butylthio and dibutylamino substituents on the reorganization energies, intermolecular electronic couplings and charge-injection barriers of IFD have been discussed. The quantum-chemical calculations combined with electron-transfer theory reveal that the incorporation of sulfur-linked side chains decreases reorganization energy associated with hole transfer and optimizes intermolecular π–π stacking, which results in excellent ambipolar charge-transport properties (μh = 1.15 cm2 V?1 s?1 and μe = 0.08 cm2 V?1 s?1); in comparison, addition of dibutylamino side chains increases intermolecular steric interactions and hinders perfect intermolecular π–π stacking, which results in the weak electronic couplings and finally causes the low intrinsic hole mobility (μh = 0.01 cm2 V?1 s?1). Furthermore, electronic spectra of butyl-IFD, butylthio-IFD and dibutylamino-IFD were simulated and compared with the reported experimental data. Calculations demonstrate that IFD-based molecules possess potential for developing novel infrared and near-infrared probe materials via suitable chemical modifications.
关键词： intrinsic electron mobility,structure–function relationship,indeno[1,2-b]fluorene-6,12-dione-based molecules,density functional theory (DFT),intrinsic hole mobility,electronic spectra
更新于2025-09-09 09:28:46
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Band structure engineering and defect control of oxides for energy applications
摘要： Metal oxides play an essential role in modern optoelectronic devices because they have many unique physical properties such as structure diversity, superb stability in solution, good catalytic activity, and simultaneous high electron conductivity and optical transmission. Therefore, they are widely used in energy-related optoelectronic applications such as photovoltaics and photoelectrochemical (PEC) fuel generation. In this review, we mainly discuss the structure engineering and defect control of oxides for energy applications, especially for transparent conducting oxides (TCOs) and oxide catalysts used for water splitting. We will review our current understanding with an emphasis on the contributions of our previous theoretical modeling, primarily based on density functional theory. In particular, we highlight our previous work: (i) the fundamental principles governing the crystal structures and the electrical and optical behaviors of TCOs; (ii) band structures and defect properties for n-type TCOs; (iii) why p-type TCOs are difficult to achieve; (iv) how to modify the band structure to achieve p-type TCOs or even bipolarly dopable TCOs; (v) the origin of the high-performance of amorphous TCOs; and (vi) band structure engineering of bulk and nano oxides for PEC water splitting. Based on the understanding above, we hope to clarify the key issues and the challenges facing the rational design of novel oxides and propose new and feasible strategies or models to improve the performance of existing oxides or design new oxides that are critical for the development of next-generation energy-related applications.
关键词： defect control,density functional theory,band-structure engineering,oxides
更新于2025-09-09 09:28:46
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Hirshfeld surface, DFT vibrational (FT-IR) and electronic (UV–vis) studies on 4-amino-1H-1,2,4-triazolium nitrate
摘要： The title molecule, 4-amino-1H-1,2,4-triazolium nitrate ([4-am-1H-124-tr]+[NO3]–), was synthesized and characterized by means of Hirshfeld surface analysis, vibrational (FT-IR) and electronic (UV–vis) studies. A density functional theory (DFT) calculations were accomplished at B3LYP level using 6-311++G(2d,2p) basis set. A detailed analysis of the intermolecular interactions via Hirshfeld surface analysis and fingerprint plots revealed that the [4-am-1H-124-tr]+[NO3]– structure is stabilized mainly by formation of O···H/H···O and N···H/H···N hydrogen bonds. However, contributions from H?H and N···O/O···N contacts were also observed. UV–vis analysis (conducted in water-phase) clearly showed that charge transfers occurred in the title molecule. The energies of HOMO and LUMO, which were active in the electronic absorption spectrum, were obtained as well. Hence, a value of 5.2605 eV was obtained as a HOMO–LUMO energy gap. A comparative analysis between the calculated and experimental vibrational frequencies was carried out and significant bands were assigned. The results indicated a good correlation between experimental and theoretical IR frequencies.
关键词： 1,2,4-triazole,Hirshfeld surface,Spectroscopic studies,Density functional theory
更新于2025-09-09 09:28:46
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Plasmons of magnesium nanodisks and their interactions with a dipole-carrying molecule
摘要： Magnesium nanostructures have recently emerged as an outstanding material with new and intriguing plasmonic properties. Here we investigate the optical properties of pristine and pyridine adsorbed magnesium nanodisks having diameter spanning in the range of 0.50 nm to 2.0 nm. We base our calculations on computationally efficient time-dependent density-functional theory calculations. Our results demonstrate that pristine magnesium nanodisks possess localized surface plasmon resonances. The adsorption of a dipole-carrying molecule significantly alters their plasmonic response due to the strong plasmon splitting, leading to new features in their optical response. We believe that magnesium nanodisks provide a versatile platform for sensing and in the design of novel ultra-sensitive plasmonic devices.
关键词： Magnesium nanodisks,Time-dependent density-functional theory,Plasmonics,Optical properties,Pyridine adsorption
更新于2025-09-09 09:28:46