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The structural and elastic properties of InSb1-xBix alloys
摘要： Based on density functional theory, the structural and elastic properties of InSb1-xBix alloys have been studied using first principle calculations. The generalized gradient approximation in the presence of spin-orbit coupling is utilized to perform the calculations presented in this paper. The calculated lattice constants of InSb1-xBix alloys are in good agreement with the available experimental data. The mechanical stability of these alloys is demonstrated using elastic constants. The ductility and brittleness of these alloys are investigated using both Poisson’s ratio and Pugh’s ratio. Moreover, the anisotropy of InSb1-xBix alloys is studied using the universal index and the 3D representation of Young's modulus. According to the obtained values of Poisson’s ratio, the InSb0.5Bi0.5 and InBi alloys are auxetic materials.
关键词： InSb1-xBix alloys,structural properties,Density functional theory,elastic properties
更新于2025-09-04 15:30:14
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Tuning the Crystal Packing and Semiconductor Electronic Properties of 7,7’-Diazaisoindigo by Side-Chain Length and Halogenation
摘要： In the last years, the 7,7’-diazaisoindigo has emerged as a promising building block for semiconductor materials. In this work, we have studied different electronic properties which can be related to the semiconducting character of a family of 7,7’-diazaisoindigo derivatives. Concretely, we have analyzed the role of halogen substituents and different-length side chains on these properties calculated by means of the Density Functional Theory. In total, sixteen halogenated and non-halogenated diazaisoindigo derivatives were investigated. Four of these compounds were also synthetized and their X-ray structures were employed as starting points for the calculation of crystal structure of the rest of the novel compounds. In general, high electron transfer rate constants and electron mobilites were calculated for the studied 7,7’-diazaisoindigo derivatives, especially for bromine derivatives and compounds with long-side chains. The origin of these high rate constants mainly resides in the strong electronic couplings found for diazaisoindigo crystals in the π-stacking direction.
关键词： 7,7’-diazaisoindigo,side chains,electron mobilities,halogen substituents,Density Functional Theory,semiconductor materials,electron transfer rate constants,π-stacking direction
更新于2025-09-04 15:30:14
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Binding of hydrogen to phosphorus dopant in phosphorus-doped diamond surfaces: A density functional theory study
摘要： Although phosphorus is an n-type donor in diamond, H impurities can bind to and passivate P. Here, H binding to a P dopant in both diamond (0 0 1) and (1 1 1) surfaces is investigated by density functional theory. The energy calculations reveal the most stable P–H complex structures for each P-doped position. P–H binding energies are the lowest for the second P doped C layer among those for four investigated P-doped C layers. H migration from on-surface to P in the second C layer is exothermic, with an energy barrier of zero, whereas that from on-surface to P below the second C layer is endothermic, with an energy barrier greater than 0.95–7.09 eV. Thus, both of binding energy and migration calculations imply that P–H complex is more likely to form when P is doped in the second C layer than when P is doped below the second C layer. Moreover, H migration energy barrier from on-surface to P below the second C layer in the (1 1 1) surface is at least 0.85 eV greater than that in the (0 0 1) surface, which indicates that P–H complex is less likely to form in (1 1 1) surface than in (0 0 1) surface.
关键词： P–H complex,Hydrogen,Density functional theory,P-doped diamond
更新于2025-09-04 15:30:14
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Structural stability and electronic properties of XTO2 (X= Cu, Ag; T=Al, Cr): an ab initio study including X vacancies and Mg doping
摘要： Ab initio density functional theory-based calculations are used to study the structural and electronic properties of CuAlO2, AgAlO2, CuCrO2, and AgCrO2 transparent conducting oxides (TCOs). The hexagonal 2H delafossite polymorph is determined here to be one of the most stable polymorphs, by comparing total energies for different structural phases. The simple antiferromagnetic configuration is chosen to model magnetic effects in CuCrO2 and AgCrO2 due to it having one of the lowest ground state total energies and containing the most semiconductor like behavior of the magnetic configurations considered. Electronic structures of 2H CuAlO2 and AgAlO2 obtained from different approximations for the exchange-correlation functional, GGA (PBE), PBE+U, PBE+mBJ, PBE+mBJ+U, and the Hybrid HSE06 are compared. Supercells are employed to model 6.25% Cu and Ag vacancies, 3.13% O vacancies, and 6.25% Mg doping replacing Al and Cr, from which structural and electronic properties are obtained and used to predict on the effectiveness of these native defects and dopant on increasing the conductivity in all TCOs studied in this work. The obtained partial density of states for the pristine systems supports a model of hole conduction in the a – b plane, perpendicular to the O – X – O dumbbells of the delafossite structure. Additionally, the partial density of states of the defective and doped systems suggest a growth environment deficient in X and saturated in O may increase conductivity in these materials.
关键词： Delafossite,Density functional theory,Transparent conducting oxides,Mg doping,Structural stability,Ab initio,Vacancies,Electronic properties
更新于2025-09-04 15:30:14
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Tailoring the Linear and Second-Order Nonlinear Optical Responses of the Titanium-MIL-125 Metal-Organic Framework through Ligand Functionalization: A First Principles Study
摘要： Density functional theory calculations have been performed to investigate the linear and second order nonlinear optical (NLO) properties of titanium-based MIL-125 metal-organic frameworks in crystalline form, in which the 1,4-benzene-dicarboxylate (BDC) linkers are modified by introducing different functional groups or by extending BDC ligand to contain two (MIL-126) and three (MIL-127) benzene rings. Our results reveal that the functionalization of BDC linker tends to increase the dielectric constants and the magnitude of birefringence of MIL-125, especially for the aminated derivatives. Correspondingly, the incorporation of substituent group will improve the phase matching performance of MIL-125. As for the second harmonic generation (SHG) susceptibility, the SHG activity of the pristine MIL-125 is comparable to KDP, which can be attributed mostly to the contributions of TiO5(OH) octahedra. It is noted that after introducing substituent group into BDC linker, the organic part will have a remarkable influence on the SHG intensity. However, the specific effect on the NLO response is dependent on the type of functional group incorporated into BDC ligand, and only the inclusion of amine group that is strongly electron-donating can obviously enhance the SHG activity of MIL-125. In addition, MIL-126 and MIL-127 with longer aromatic linking unit are not suitable to act as NLO materials due to their poor phase matching abilities, but they are the promising candidates for the low dielectric constant materials. The present study can provide theoretical insights to design new second-order NLO materials based on MIL-125.
关键词： Nonlinear Optical Properties,Density Functional Theory,Hybrid Materials,Ligand Functionalization,Metal-Organic Framework,Plasmonics,Optical,Magnetic
更新于2025-09-04 15:30:14
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Conserving approximations in cavity quantum electrodynamics: Implications for density functional theory of electron-photon systems
摘要： By analyzing the many-body problem for nonrelativistic electrons strongly coupled to photon modes of a microcavity I derive the exact momentum/force balance equation for cavity quantum electrodynamics. Implications of this equation for the electron self-energy and the exchange-correlation potential of the quantum electrodynamic time-dependent density functional (QED-TDDFT) are discussed. In particular I generalize the concept of (cid:2) derivability to construct approximations which ensure the correct momentum balance. It is shown that a recently proposed optimized effective potential approximation for QED-TDDFT is conserving, and its possible improvements are discussed.
关键词： cavity quantum electrodynamics,density functional theory,conserving approximations,momentum balance,electron-photon systems
更新于2025-09-04 15:30:14
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Heterodimer on MgO
摘要： We report on the magnetic properties of HoCo dimers as a model system for the smallest intermetallic compound of a lanthanide and a transition metal atom. The dimers are adsorbed on ultrathin MgO(100) films grown on Ag(100). New for 4f elements, we detect inelastic excitations with scanning tunneling spectroscopy and prove their magnetic origin by applying an external magnetic field. In combination with density functional theory and spin Hamiltonian analysis, we determine the magnetic level distribution, as well as sign and magnitude of the exchange interaction between the two atoms. In contrast to typical 4f ? 3d bulk compounds, we find ferromagnetic coupling in the dimer.
关键词： ferromagnetic coupling,heterodimer,density functional theory,spin excitations,scanning tunneling spectroscopy
更新于2025-09-04 15:30:14
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Effects of Varying the Benzannulation Site and π Conjugation of the Cyclometalating Ligand on the Photophysics and Reverse Saturable Absorption of Monocationic Iridium(III) Complexes
摘要： A series of monocationic iridium(III) complexes, [Ir(C^N)2(pqu)]+PF6? [pqu = 2-(pyridin-2-yl)quinoline, C^N = 2-phenylquinoline (1), 3-phenylisoquinoline (2), 1-phenylisoquinoline (3), benzo[h]quinoline (4), 2-(pyridin-2-yl)naphthalene (5), 1-(pyridin-2-yl)naphthalene (6), 2-(phenanthren-9-yl)pyridine (7), 2-phenylbenzo[g]quinoline (8), 2-(naphthalen-2-yl)quinoline (9), and 2-(naphthalen-2-yl)benzo[g]quinoline (10)], were synthesized in this work. These complexes bear C^N ligands with varied degrees of π conjugation and sites of benzannulation, allowing for elucidation of the effects of the benzannulation site at the C^N ligand on the photophysics of the complexes. Ultraviolet?visible (UV?vis) absorption and emission of the complexes were systematically investigated via spectroscopic techniques and time-dependent density functional theory calculations. Their triplet excited-state absorption and reverse saturable absorption (RSA) were studied by nanosecond transient absorption (TA) spectroscopy and nonlinear transmission techniques. The fusion of phenyl ring(s) to the phenyl ring or the 4 and 5 positions of the pyridyl ring of the C^N ligand resulted in red-shifted UV?vis absorption and emission spectra in complexes 2, 5?7, 9, and 10 compared to those of the parent complex 0, while their triplet lifetimes and emission quantum yields were significantly reduced. In contrast, the fusion of one phenyl ring to the other sites of the pyridyl group of the C^N ligand showed an insignificant impact on the energies of the lowest singlet (S1) and triplet (T1) excited states in complexes 1, 3, and 4 but noticeably affected their TA spectral features. The fusion of the naphthyl group to the 5 and 6 and positions at the pyridyl ring did not influence the S1 energy of complex 8 but altered the nature of the T1 states in 8 and 10 by switching them to the benzo[g]quinoline-localized 3π,π* state, which resulted in completely different emission and TA spectra in these two complexes. The site-dependent variations of the ground- and excited-state absorption induced strong but varied RSA from these complexes for 4.1-ns laser pulses at 532 nm, with the RSA strength decreasing in the trend of 3 > 7 ≈ 4 ≈ 9 ≈ 6 > 8 ≈ 1 ≈ 2 ≈ 5 > 10.
关键词： iridium(III) complexes,time-dependent density functional theory,spectroscopic techniques,photophysics,reverse saturable absorption,benzannulation
更新于2025-09-04 15:30:14
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Ab-initio study on electronic and magnetic properties of (Ga,Co) co-doped ZnO
摘要： Using first-principles calculations based on density functional theory within GGA formalism, we have studied the electronic structure and magnetic properties of (Ga,Co) co-doped ZnO system. The effect of impurity distances on ferromagnetic and antiferromagnetic ground state in Co0.056Zn0.944O has been studied. For the closest Co-Co distance, a ferromagnetic ground state with total magnetic moment of ~3.00μμ’ per Co atom has been found. The electronic structure also displays a nearly halfmetallic order. Conversely, for the farthest Co-Co distance an antiferromagnetic ground state was found for Co0.056Zn0.944O. When Zn2+ ions are replaced by Ga ions in Co0.056Zn0.944O, the new (Ga,Co) co-doped ZnO system is more energetically stable. It has also been found that Ga-doping reduces the Co0.056Zn0.944O band gap due to the sp-d exchange interactions, which is in good agreement with the experimental data. Moreover, the Ga-doping changes the nearly halmetallic order of Co0.056Zn0.944O to metallic. Results also show that Ga0.029Co0.056Zn0.915O is still ferromagnetic with a total magnetic moment of ~3.00μμ’ per Co atom. It was also found that the ferromagnetic ground state in (Ga,Co) co-doped ZnO vanishes as Ga concentration increases.
关键词： GGA formalism,(Ga,ab-initio,density functional theory,electronic structure,Co) co-doped ZnO,magnetic properties
更新于2025-09-04 15:30:14
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-SiC
摘要： Optical charge state switching was previously observed in photoluminescence experiments for the divacancy defect in 4H-SiC. The participating dark charge state could not be identified with certainty. We use constrained density-functional theory to investigate the mechanism of charge state conversion from the bright neutral charge state of the divacancy defect to the positive and negative charge states including corresponding recovery of the neutral charge state. While we can confirm that the positive charge state is dark, we do not find evidence that the negative charge state is dark. We compute similar absorption energies required for conversion of the neutral defect to both charge states. However, the formation of the positive charge state requires a series of excitations involving a 2-photon excitation, while the creation of the negative charge state is achieved through a single 2-photon process. Calculated absorption energies for the recovery of the neutral defect from the positive charge state fit the experimental value better than those from the negative charge state. Defect formation energies as a function of the Fermi energy show a very small Fermi energy range in which the negative charge state is most stable, while the positive charge state exhibits a wide stability range. Overall, our computational results give more support to the identification of the dark charge state as the positive over the negative charge state in the mechanism of optical charge state switching.
关键词： divacancy defect,optical charge state switching,constrained density-functional theory,photoluminescence,4H-SiC
更新于2025-09-04 15:30:14