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Synthesis, photophysical properties and DFT studies of the pyridine-imidazole (PyIm) Cu(I) complexes: Impact of the pyridine ring functionalized by different substituents
摘要： A series of the pyridine-imidazole (PyIm) Cu(I) complexes with different substituents (bromide (P1), methyl (P2), and phenyl (P3)) attached on the pyridine ring are synthesized and characterized. All the complexes show the typical metal-to-ligand charge transfer (MLCT) absorption in the visible region. Complex P1 with an electron-withdrawing substituent on the pyridine ring, e.g., a bromine group, shows a red shift of the emission wavelength. Conversely, an electron-donating substituent on the pyridine ring in complex P2, e.g., a methyl group, shifts the emission to longer wavelength. Similarly, complex P3 containing the extended π-conjugation system of the ligand also exhibits a red shift of the emission wavelength. All of the complexes exhibit efficient green-yellow emission in PMMA films at room temperature with emission wavelength of 547–569 nm and quantum yields of 24.8–53.0%. Meanwhile, DFT and TDDFT methods were employed to explain the photophysical properties.
关键词： Pyridine-imidazole,Copper (I) complex,Metal-to-ligand charge transfer,Molar extinction coefficient,Density functional theory
更新于2025-09-23 15:22:29
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Elastic and optoelectronic properties of CaTa2O6 compounds: Cubic and orthorhombic phases
摘要： Using first principles density functional theory (DFT) simulations, the structural, electronic, optical and elastic properties of CaTa2O6 oxide for cubic and orthorhombic phases are studied by highly accurate (FP-LAPW) method within the GGA + U approximation. The calculated lattice parameters are consistent with available experimental data. The electronic band structure calculations have shown that the band gaps in CaTa2O6 are equal to 3.08 eV and 4.40 eV for the cubic and orthorhombic structures, respectively. For both the phases the main optical properties, e.g., absorption coefficient, dielectric constant, energy loss function, and reflectivity, refractive index, and extinction coefficient are calculated and discussed in detail in the spectral range 0-14 eV. Cubic and orthorhombic phases exhibit significantly different optical characteristics. The electronic bonding characters of CaTa2O6 with different symmetries are explored via charge density distribution mapping. Strong covalent bonding character dominates in both the phases of CaTa2O6. Elastic properties of CaTa2O6 for cubic and orthorhombic phases are also investigated. The stress strain method is used for the determination of elastic constants in both the phases. The bulk modulus, shear modulus, Young’s modulus, along with the important elastic anisotropy factors and Poisson’s ratio are studied in detail.
关键词： First principles density functional theory,GGA+U approximation,FP-LAPW method,Optical constants,Electronic band structure,electro technical materials
更新于2025-09-23 15:22:29
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Doping of Monolayer Transition Metal Dichalcogenides via Physisorption of Aromatic Solvent Molecules
摘要： Two-dimensional (2D) transition metal dichalcogenides (TMDs) recently emerged as novel materials displaying a wide variety of physico-chemical properties that render them unique scaffolds for high-performance (opto)electronics. The controlled physisorption of molecules on the TMD surface is a viable approach to tune their optical and electronic properties. Solvents, made of small aromatic molecules, are frequently employed for the cleaning of the 2D materials or as 'dispersant' for their chemical functionalization with larger (macro)molecules, without considering their potential key effect in locally modifying the characteristics of 2D materials. In this work, we demonstrate how the electronic and optical properties of mechanically exfoliated monolayer of MoS2 and WSe2 are modified when physically interacting with small aromatic molecules of common solvents. Low-temperature photoluminescence (PL) spectra recorded at 78 K revealed that physisorbed benzene derivatives could modulate the charge carrier density in monolayer TMDs, hence affecting the switching between neutral exciton and trion (charged exciton). By combining experimental evidences with DFT calculations, we confirm that charge transfer doping on TMDs depends not only on difference in chemical potential between molecules and 2D materials, but also on the thermodynamic stability of physisorption. Our results provide unambiguous evidence of the great potential of optical and electrical tuning of monolayer MoS2 and WSe2 by physisorption of small aromatic solvent molecules, which is highly relevant both for fundamental studies and more device applied purposes.
关键词： transition metal dichalcogenides,aromatic molecules,Density Functional Theory,doping,photoluminescence
更新于2025-09-23 15:22:29
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Unusual Electronic States and Superconducting Proximity Effect of Bi Films Modulated by NbSe2 Substrate
摘要： Heterostructures of two-dimensional layered materials can be functionalized with exotic phenomena that are unpresented with each constituting component. The interface effect plays a key role in determining the electronic properties of the heterostructure, whose characterization requires a correlation with the morphology with atomic-scale precision. Here, we report an investigation on the electronic properties of few-layer Bi(110) films mediated by NbSe2 substrate. By utilizing scanning tunneling microscopy and spectroscopy, we show a significant variation of the density of states at different Bi film thicknesses, resulting in an unusual superconducting proximity effect that deviates from the conventional monotonous decay behavior. Moreover, the electronic states of the Bi films are also prominently modulated by the Moiré pattern spatially. With first-principles calculations, we illuminate these findings as the results of covalent-like quasi-bonds formed at the Bi/NbSe2 interface, which profoundly alter the charge distributions in the Bi films. Our study indicates a viable way of modulating the electronic properties of ultrathin films by quasi-covalent interfacial couplings beyond conventional van der Waals interactions.
关键词： few-layers bismuth(110),two-dimensional heterostructures,thickness dependence,scanning tunneling microscopy,density functional theory calculations,covalent-like quasi-bonds,proximity effect
更新于2025-09-23 15:22:29
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Constructing CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> and CH <sub/>3</sub> NH <sub/>3</sub> PbBr <sub/>3</sub> Perovskite Thin Film Electronic Structure from Single Crystal Band Structure Measurements
摘要： Photovoltaic cells based on halide perovskites and possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential, but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3) we reveal the band dispersion in two high symmetry directions, and identify the global valence band maxima. With these benchmark data, we construct 'standard' photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature of determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.
关键词： single crystal and thin film perovskites,angle-resolved photoemission,low-energy electron diffraction and density functional theory
更新于2025-09-23 15:22:29
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Ab-Initio Prediction of Intrinsic Half-Metallicity in Binary Alkali–Metal Chalcogenides: KX (X=S, Se and Te)
摘要： First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic and magnetic properties of KX (X ? S, Se and Te) binary alkali–metal chalcogenides compounds. These compounds in different crystalline phases, NaCl (B1), CsCl (B2), ZB (B3), NiAs (B81T, WZ (B4) and Pnma, were calculated within the generalized gradient approximation (GGA-PBE) and the modified Becke–Johnson approach (mBJ-GGA-PBE) for the exchange–correlation energy and potential. We found that the most stable phase for the KX binary compounds is the nonmagnetic Pnma phase. The calculated lattice parameters, bulk moduli, their first-pressure derivatives and internal parameters are in good agreement with the other theoretical data. The electronic band structure and density of states show that half-metallic and magnetic character arises, which can be attributed to the presence of spin-polarized p orbitals in the group VI elements. KX (X ? S, Se and Te) compounds, except for KSe and KTe in the CsCl and NiAs phases, show HM character in all phases, with an integer magnetic moment of 1 (cid:1)B per formula unit and HM gaps.
关键词： alkali metals,Density functional theory,half-metals,chalcogenides,ferromagnetism
更新于2025-09-23 15:22:29
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Phase Transition in Two-dimensional Tellurene under Mechanical Strain Modulation
摘要： We carry out computational simulations based on density functional theory (DFT) to investigate different phases of two-dimensional (2-D) tellurene. These phases are classified by their characteristic space groups and symmetry elements. Correlations of these phases to the bulk crystalline tellurium structure are also illustrated. Our specific interests include mechanical property calculations for different phases and the possible phase transitions between them. Simulation results show that these 2-D Te phases have very different elastic moduli due to their different atomic bonding and relaxed structures. Moreover, compression along the in-plane directions facilitates the α → β phase transition, while in-plane tensile strains always make the α-phase more stable than the β-phase. However, the energy difference between the two phases is comparable to or even much smaller than the thermal energy kT, depending on the in-plane strain direction. We find that further increase of the tensile strain along the chain direction beyond a critical value, ca. 12%, may lead to a possible α → γ phase transition. As the tensile strain is above 15%, the γ-phase will be more stable than the α-phase, accompanied by a further reduced transition energy barrier.
关键词： phase transition,elastic modulus,Tellurene,strain engineering,density functional theory (DFT),2-D materials
更新于2025-09-23 15:22:29
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Mixing Thermodynamics and Photocatalytic Properties of GaP-ZnS solid solutions
摘要： Preparation of solid solutions represents an effective means to improve the photocatalytic properties of semiconductor-based materials. Nevertheless, the effects of site-occupancy disorder on the functional properties of materials are difficult to predict and consequently many experimental trials may be required before achieving enhanced photocatalytic activity. Here, first-principles methods are employed to estimate the mixing free energy and the structural and electronic properties of (GaP)x(ZnS)1?x solid solutions. The method relies on a multi-configurational supercell approach that takes into account the configurational and vibrational contributions to the free energy. Phase competition among the zinc-blende and wurtzite polymorphs is also considered. Overall excellent agreement with the available experimental data is demonstrated, namely: 1) zinc-blende is energetically most favorable, 2) the solid solution energy band gap lies within the 2–3 eV range, and 3) the energy band gap of the solid solution is direct for compositions x ≤ 75%. It is found that at ambient conditions, (GaP)x(ZnS)1?x solid solutions with x ≈ 25%, 50% and 75% render promising hydrogen evolution photocatalysts for water splitting under visible light, owing to their favorable energy band gaps and band levels relative to vacuum.
关键词： multiconfigurational supercell approach,semiconductor solid solutions,density functional theory calculations,photocatalytic materials
更新于2025-09-23 15:22:29
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Prediction of Second-Order Nonlinear Optical Properties of D–π–A Compounds Containing Novel Fluorene Derivatives: A Promising Route to Giant Hyperpolarizabilities
摘要： Herein, ?rst attempt has been made to utilize ?uorene-based dye-sensitized solar cell (DSSCs) dye JK-201 as potential nonlinear optical (NLO) material and for the theoretical designing of novel NLO chromophores JK-D1–JK-D12. DFT/TDDFT calculations were performed to compute the effect of p-linkers and acceptors-steered modulation on electronic, photophysical and NLO properties of JK-201 and JK-D1–JK-D12. Results illustrate that computed kmax (484.74 nm) and experimentally calculated kmax (481 nm) of JK-201 was found in good agreement. Maximum red shifted absorption spectrum was observed in JK-D12 with 599.38 nm. JK-D1–JK-D12 showed narrow energy gap and broader absorption spectrum as compared to JK-201. NBO analysis con?rmed the formation of charge separation state due to robust range of electrons/charge transfer from donor to acceptor via p-bridge. Giant NLO response was observed in all compounds. Particularly, JK-D12 displayed surprisingly large hai and btot computed 1376.74 (a.u.) and 405,731.84 (a.u.) respectively. Although literature is ?ooded with D–p–A compounds investigated for their DSSCs properties, but research reports on their NLO properties and utilization as NLO materials are completely deserted. Our research will open new horizons to explore DSSCs materials for NLO applications. This theoretical framework also exposed that ?uorene-substituted chromophores are excellent NLO candidates for modern hi-tech applications.
关键词： D–p–A organic chromophores,Acceptor units,Molecular modeling,Density functional theory,NLO response properties,p-Conjugated linkers
更新于2025-09-23 15:22:29
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Generalized gradient approximation exchange energy functional with near-best semilocal performance
摘要： We develop and validate a non-empirical generalized gradient approximation (GGA) exchange (X) density functional which performs as well as the SCAN meta-GGA on standard thermochemistry tests. Additionally, the new functional (“NCAP”) yields Kohn-Sham eigenvalues that are useful approximations of the density functional theory (DFT) ionization potential theorem values by inclusion of a systematic derivative discontinuity shift of the X potential. NCAP also enables time-dependent DFT (TD-DFT) calculations of good quality polarizabilities, hyper-polarizabilities, and one-fermion excited states without modification (calculated or ad hoc) of the long-range behavior of the exchange potential or other patches. NCAP is constructed by reconsidering the imposition of the asymptotic correctness of the X potential (-1/r) as a constraint. Inclusion of derivative discontinuity and approximate integer self-interaction correction treatments along with first-principles determination of the effective second-order gradient expansion coefficient yields a major advance over our earlier correct asymptotic potential functional [“CAP”; J. Chem. Phys. 142, 054105 (2015)]. The new functional reduces a spurious bump in the CAP atomic exchange potential and moves it to distances irrelevantly far from the nucleus (outside the tail of essentially all practical basis functions). It therefore has nearly correct atomic exchange-potential behavior out to rather large finite distances r from the nucleus but eventually goes as ? c / r with an estimated value for the constant c of around 0.3, so as to achieve other important properties of exact DFT exchange within the restrictions of the GGA form. We illustrate the results with the Ne atom optimized effective potentials and with standard molecular benchmark test data sets for thermochemical, structural and response properties.
关键词： hyperpolarizabilities,excitation energies,Density functional theory,exchange potential asymptotic behavior,polarizabilities,exchange-correlation functional
更新于2025-09-23 15:21:21