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Infrared reflectance, transmittance, and emittance spectra of MgO from first principles
摘要： By using density functional theory calculations we determined the influence of anharmonic effects on the infrared reflectance, transmittance, and emittance of MgO. The goal is to determine the limit of validity of a perturbative (multiphonon) approach. MgO is chosen as a test material because of the availability of different kinds of radiative properties measured experimentally. Nonanalytic terms of the three-phonon scattering coefficients are explicitly calculated and do not provide measurable effects. The agreement is overall very good to such an extent that, already at room temperature, one can clearly identify regions in which four-phonon scattering processes are dominant with respect to the three-phonon ones. The influence of isotopic disorder at cryogenic temperatures is also settled.
关键词： emittance,transmittance,density functional theory,MgO,infrared reflectance,anharmonic effects,phonon-phonon interactions
更新于2025-09-10 09:29:36
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Enhanced H2S sensing performance of cobalt doped free-standing TiO2 nanotube array film and theoretical simulation based on density functional theory
摘要： A cobalt doped free-standing TiO2 nanotube (Co-doped TiNT) array film was firstly synthesized by a one-step anodization followed by immersion method. The characterization analysis results of TiNT with the field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) proved that the doped cobalt ions had entered into the lattice of TiO2. Subsequently, the Co-doped TiNT gas sensors with different concentration of cobalt ions were developed for testing the gas-sensing properties for H2S. Compared with the undoped one, by 0.1 M Co-doping operation, working under the temperature of 300 °C, the Co-doped TiNT gas sensor was demonstrated the following superiorities: the response time and recovery time were 14 s and 4 s, which were shortened by 36.4% and 33.3%, respectively. Moreover, the Co-doped TiNT gas sensor with superior selectivity, stability and repeatability, reached the response value at 199.16 for 50 ppm H2S, which was improved by 7.6 times. Finally, based on the density functional theory (DFT), the calculated band gap of the Co-doped TiO2 decreased from 2.285 eV to 1.418 eV with a 38% decline. The mechanism simulation explained the obtained promotions in the gas sensing properties of the Co-doped TiNT gas sensor.
关键词： Cobalt ion doping,H2S gas sensor,Highly sensitivity,TiO2 nanotube array film,Density functional theory
更新于2025-09-10 09:29:36
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First-principles investigation on the interlayer doping of SnSe2 bilayer
摘要： Using density functional theory calculations, we systematically investigated the effects of numbers and types of transition metals (TM) on the magnetic property of SnSe2 bilayer nanosheet. Our results revealed that, when one TM is introduced into the interlayer, the magnetic moment induced by the Co and Ni is tiny while it is largely strengthened with the doping of V, Cr, Mn, and Fe. When two TMs are inserted into the interlayer, Vand Cr make the system change into a weak antiferromagnetism (AFM) state while Mn-, Fe-, Co-doped systems display a weak ferromagnetism (FM) ground state. These FM states have the magnetic moments which double those of the one TM–doping systems. With the TM numbers further increasing to four, the robust AFM and FM features appear with the doping of Fe and Mn, respectively. Ni cannot induce any magnetism whatever the numbers of Ni are filling in. Interestingly, with the increase of the numbers of dopants, transitions from FM to AFM and AFM to FM are predicted to be realized on Fe-SnSe2 and Cr-SnSe2 systems, respectively. This kind of transition may be important for the applications in spintronic devices.
关键词： Interlayer doping,Spintronics application,Density functional theory,Antiferromagnetism,Modeling and simulation,Ferromagnetism,SnSe2
更新于2025-09-10 09:29:36
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Strain-Tunable Electronic Properties and Band Alignments in GaTe/C2N Heterostructure: a First-Principles Calculation
摘要： Recently, GaTe and C2N monolayers have been successfully synthesized and show fascinating electronic and optical properties. Such hybrid of GaTe with C2N may induce new novel physical properties. In this work, we perform ab initio simulations on the structural, electronic, and optical properties of the GaTe/C2N van der Waals (vdW) heterostructure. Our calculations show that the GaTe/C2N vdW heterostructure is an indirect-gap semiconductor with type-II band alignment, facilitating an effective separation of photogenerated carriers. Intriguingly, it also presents enhanced visible-UV light absorption compared to its components and can be tailored to be a good photocatalyst for water splitting at certain pH by applying vertical strains. Further, we explore specifically the adsorption and decomposition of water molecules on the surface of C2N layer in the heterostructure and the subsequent formation of hydrogen, which reveals the mechanism of photocatalytic hydrogen production on the 2D GaTe/C2N heterostructure. Moreover, it is found that in-plane biaxial strains can induce indirect-direct-indirect, semiconductor-metal, and type II to type I or type III transitions. These interesting results make the GaTe/C2N vdW heterostructure a promising candidate for applications in next generation of multifunctional optoelectronic devices.
关键词： Strains,Density functional theory,Heterostructure,Multifunctional devices,GaTe/C2N
更新于2025-09-10 09:29:36
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Elucidating the Non-Radiative Deactivation Pathways in a Cationic Iridium Complex with 2,4-di(1 <i>H</i> -pyrazol-1-yl)Pyridine as the Ancillary Ligand
摘要： Deep insight into the non-radiative deactivation pathways in phosphorescent cationic iridium complexes is critically important for developing efficient blue-emitting complexes toward advanced applications. Here, we report the synthesis, photophysical and electrochemical characterizations of a blue-green-emitting cationic iridium complex [Ir(ppy)2(bipzpy)]PF6 (Hppy is 2-phenylpyridine and bipzpy is 2,4-di(1H-pyrazol-1-yl)pyridine). The non-radiative deactivation pathways in [Ir(ppy)2(bipzpy)]PF6 have been elucidated through extensive density functional theory calculations. The calculations reveal that the higher-lying charge-transfer (CT) state in [Ir(ppy)2(bipzpy)]PF6, which arises from Ir/ppy→bipzpy transitions, favors non-radiative deactivation because of its large structural distortion compared to the ground state. Both the CT state and the dark metal-centered (3MC) state can be thermally accessed by the lowest-lying emitting triplet state at room temperature, with the former being much more easily accessible, which causes additional non-radiative deactivations for the emitting triplet state. The active roles of the CT and 3MC states in the non-radiative deactivation pathways are, for the first time, confirmed in such blue-emitting complexes with pzpy-type ancillary ligands (pzpy is 2-(1H-pyrazol-1-yl)pyridine).
关键词： charge-transfer state,metal-centered state,density functional theory,blue-emitting complexes,phosphorescent cationic iridium complexes,non-radiative deactivation
更新于2025-09-10 09:29:36
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Efficient calculation of (resonance) Raman spectra and excitation profiles with real-time propagation
摘要： We investigate approaches for the calculation of (resonance) Raman spectra in a real-time time-dependent density functional theory (RT-TDDFT) framework. Several short time approximations to the Kramers, Heisenberg, and Dirac polarizability tensor are examined with regard to the calculation of resonance Raman spectra: One relies on a Placzek type expansion of the electronic polarizability and the other one relies on the excited state gradient method. The first one is shown to be in agreement with an approach based on perturbation theory in the case of a weak δ-pulse perturbation. The latter is newly applied in a real time propagation framework, enabled by the use of Pad′e approximants to the Fourier transform which allow for a sufficient resolution in the frequency domain. An analysis of the performance of Pad′e approximants is given. All approaches were found to be in good agreement for uracil and R-methyloxirane. Moreover it is shown how RT-TDDFT can be used to calculate Raman excitation profiles efficiently.
关键词： Raman spectra,Pad′e approximants,excitation profiles,time-dependent density functional theory,real-time propagation
更新于2025-09-10 09:29:36
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Strength and toughness anisotropy in hexagonal boron nitride: An atomistic picture
摘要： Strength and toughness are two crucial mechanical properties of a solid that determine its ability to function reliably without undergoing failure in extreme conditions. While hexagonal boron nitride (hBN) is known to be elastically isotropic in the linear regime of mechanical deformation, its directional response to extreme mechanical loading remains less understood. Here, using a combination of density functional theory calculations and molecular dynamics simulations, we show that strength and crack nucleation toughness of pristine hBN are strongly anisotropic and chirality dependent. They vary nonlinearly with the chirality of the lattice under symmetry breaking deformation, and the anisotropic behavior is retained over a large temperature range with a decreasing trend at higher temperatures. An atomistic analysis reveals that bond deformation and associated distortion of electron density are nonuniform in the nonlinear regime of mechanical deformation, irrespective of the loading direction. This nonuniformity forms the physical basis for the observed anisotropy under static conditions, whereas reduction in nonuniformity and thermal softening reduce anisotropy at higher temperatures. The chirality-dependent anisotropic effects are well predicted by inverse cubic polynomials.
关键词： chirality,anisotropy,hexagonal boron nitride,molecular dynamics simulations,density functional theory,strength,toughness
更新于2025-09-10 09:29:36
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The origin of low bandgap and ferroelectricity of a co-doped BaTiO <sub/>3</sub>
摘要： We recently demonstrated the lowest bandgap ferroelectric, for visible light absorption in BaTi1?x(Mn1/2Nb1/2)xO3, a promising candidate material optoelectronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.
关键词： ferroelectricity,Mn doping,x-ray spectroscopies,bandgap,density functional theory,BaTiO3
更新于2025-09-10 09:29:36
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[Advances in Experimental Medicine and Biology] Glycobiophysics Volume 1104 || Synchrotron-Radiation Vacuum-Ultraviolet Circular-Dichroism Spectroscopy for Characterizing the Structure of Saccharides
摘要： Circular-dichroism (CD) spectroscopy is a powerful tool for analyzing the structures of chiral molecules and biomolecules. The development of CD instruments using synchrotron radiation has greatly expanded the utility of this method by extending the spectra to the vacuum-ultraviolet (VUV) region below 190 nm and thereby yielding information that is unobtainable by conventional CD instruments. This technique is especially advantageous for monitoring the structure of saccharides that contain hydroxy and acetal groups with high-energy transitions in the VUV region. Combining VUVCD spectra with theoretical calculations provides new insight into the contributions of anomeric hydroxy groups and rotational isomers of hydroxymethyl groups to the dynamics, intramolecular hydrogen bonds, and hydration of saccharides in aqueous solution.
关键词： Glycoprotein,Hydration,Circular dichroism,Synchrotron radiation,Time-dependent density functional theory,Molecular dynamics simulation,Saccharide,Intramolecular hydrogen bond,Solution structure,Structural dynamics,Vacuum ultraviolet,Glycosaminoglycan
更新于2025-09-10 09:29:36
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Ab initio Calculations of Phonon Dispersion in CdGa2S4
摘要： The phonon spectrum of CdGa2S4 has been experimentally investigated by Raman spectroscopy and theoretically analyzed using the density functional theory (DFT). Eleven active Raman modes (at 83, 135, 165, 219, 243, 260, 310, 322, 352, 361, and 392 cm–1) have been detected and identified. The identification of all vibrational modes is based on consideration of the point symmetry group. The results are compared with the existing experimental IR spectroscopy and Raman scattering data.
关键词： Raman spectroscopy,phonon dispersion,CdGa2S4,lattice dynamics,density functional theory
更新于2025-09-10 09:29:36