Relevant Electronic Structure Research Articles

The effect of substitutional doping of Yb2+ on structural, electronic, and optical properties of CsCaX 3 (X: Cl, Br, I) phosphors: a first-principles study

Using first-principles calculations, the effects of Yb2+ substitutional doping on structural, electronic, and optical properties of a series of perovskite compounds CsCaX 3 (X: Cl, Br, I), have been investigated. We employed generalized gradient approximation (GGA) and HSE hybrid functional to study the electronic and optical properties. A series of pristine CsCaX 3 (X: Cl, Br, I) is characterized as a non-magnetic insulator with indirect bandgap perovskite materials. These phosphor materials are suitable candidates for doping with lanthanide series elements to tune their electronic bandgaps according to our requirements because of their wide bandgaps. The calculated electronic bandgaps of CsCaX 3 (X: Cl, Br, I) are 3.7 eV (GGA) and 4.5 eV (HSE) for CsCaI3, 4.5 eV (GGA) and 5.3 eV (HSE) for CsCaBr3, and 5.4 eV (GGA) and 6.4 eV (HSE) for CsCaCl3. According to formation energies, the Yb2+ doped at the Ca-site is thermodynamically more stable as compared to all possible atomic sites. The electronic band structures show that the Yb2+ doping induces defective states within the bandgaps of pristine CsCaX 3 (X: Cl, Br, I). As a result, the Yb2+ doped CsCaX 3 (X: Cl, Br, I) become the direct bandgap semiconductors. The defective states above the valence band maximum are produced due to the f-orbital of the Yb atom. The impurity states near the conduction band minimum are induced due to the major contribution of d-orbital of the Yb atom and the minor contribution of s-orbital of the Cs atom. The real and imaginary parts of the dielectric function, optical reflectivity, electron energy loss spectrum, extinction coefficient, and refractive index of pristine and Yb2+ doped CsCaX 3 (X: Cl, Br, I) were studied. The optical dispersion results of dielectric susceptibility closely match their relevant electronic structure and align with previously reported theoretical and experimental data. We conclude that the Yb2+ doped CsCaX 3 (X: Cl, Br, I) are appealing candidates for optoelectronic devices.

Phase stability, elasticity, hardness and electronic structures for binary MnBm (M = Ni, Cr, Mo, W, n = 23, 5, 3, 1, m = 6, 3, 2, 1) borides: a comprehensive study using first principles

ABSTRACTPhase stability, elasticity, hardness and relevant electronic structures of MnBm(M = Ni, Cr, Mo, W, n = 23,5,3,1, m = 6,3,2,1) binary borides have been investigated by first-principles calculations. The linear relationships between the formation enthalpies and their boron content x are found in 4 kinds of MnBm. The formation enthalpies gradually decrease with the increase of B content. The calculated elastic constants indicate that the MnBm (M = Cr, Mo and W) borides change gradually from ductility to brittleness with the increase of B content, while the NinBm borides show a ductile nature. The sequence in regard to hardness is CrnBm>MonBm (and WnBm) > NinBm. Electronic structure analysis shows that the variation trend of N(EF) is in accordance with that of formation enthalpies. Strong M–B bonds and pseudogap between the peaks at both side of the fermi energy are found to play important roles in the hardness and phase stability of these borides.

Understanding structure of small $${\hbox {TiO}}_2$$ nanoparticles and adsorption mechanisms of PbS quantum dots for solid-state applications: a combined theoretical and experimental study

A combined theoretical and experimental study on a series of $${\hbox {TiO}}_{2}$$ , lead sulfide (PbS) and PbS@TiO $$_{2}$$ nanocomposites was performed. $${\hbox {TiO}}_{2}$$ structures were stabilized with simulated annealing using molecular dynamics at the ReaxFF level. A density functional theory study elucidated relevant electronic structure properties. We performed the study for a series of $${\hbox {TiO}}_2$$ ) $$_{n}$$ , where $$n =18$$ , 28, 38, 76 and 114. Band gaps ranging from 1.2 to 2.2 eV were found. This range was attributed to the size of the $${\hbox {TiO}}_2$$ cluster models used in the calculations, and some models became metallic at smaller sizes. We synthesized $${\hbox {TiO}}_2$$ nanoparticles of anatase (101) facet, which were characterized with pair distribution functions, in excellent agreement with the theoretical results. We explored the possibility to anchor a PbS quantum dot with a $${\hbox {TiO}}_2$$ model system. This intermolecular interaction was relevant, since the composite material could be used in solid-state devices' applications, in which stability in the formation of the $${\hbox {PbS}}/{\hbox {TiO}}_{2}$$ interface plays an important role for the device performance. The possibility to form a PbS@TiO $$_{2}$$ composite material was evidenced, via a covalent interaction, with contributions of the van der Waals type.

Geometric structure and electronic properties of wurtzite GaN/HfO2 interface: A first-principles study

III-V interface with high-k oxide, especially HfO2, is crucial to the development of high mobility microelectronic devices. In this work, we systematically investigated the wurtzite GaN/cubic HfO2 interface based on the first-principles calculations with density functional theory in terms of the geometric structure and electronic properties. In order to mimic the high-k growth conditions, the interfacial oxygen contents in the slab interface models varied to study the interface stability and the relevant electronic structures. It is found that the oxygen rich interface, i.e., oxygen content of 83.3% (O5), shows the most stability in a large range of the oxygen chemical potential from 0 eV to −4.34 eV. Through the calculations of local density of states and Bader charge analysis, we noticed that increasing the interfacial oxygen content leads to the increase of the valence band offset (VBO) and the decrease of the conduction band offset (CBO), respectively. More importantly, interface O5 displays a promising VBO (0.86 eV) and CBO (1.34 eV), which meets the industrial requirements to confine the carrier in the III-V channel materials. Furthermore, no interfacial gap states are observed in interface O5, indicating that O5 is free of Fermi level pinning. This theoretical exploration suggests that varying oxygen content at the interface could result in the optimal interface for the applications of high mobility electronic devices.

Carbon Nanotube-Based Organic Thermoelectric Materials for Energy Harvesting.

Carbon nanotubes (CNTs) have attracted much attention in developing high-performance, low-cost, flexible thermoelectric (TE) materials because of their great electrical and mechanical properties. Theory predicts that one-dimensional semiconductors have natural advantages in TE fields. During the past few decades, remarkable progress has been achieved in both theory and experiments. What is more important is that CNTs have shown desirable features for either n-type or p-type TE properties through specific strategies. Up to now, CNT‒polymer hybrids have held the record for TE performance in organic materials, which means they can potentially be used in high-performance TE applications and flexible electronic devices. In this review, we intend to focus on the intrinsic TE properties of both n-type and p-type CNTs and effective TE enhanced strategies. Furthermore, the current trends for developing CNT-based and CNT‒polymer-based high TE performance organic materials are discussed, followed by an overview of the relevant electronic structure‒TE property relationship. Finally, models for evaluating the TE properties are provided and a few representative samples of CNT‒polymer composites with high TE performance are highlighted.

Theoretical study on the phase stability, elasticity, hardness and electronic structures of Ni–P compounds

ABSTRACTA systematic investigation concerned with phase stability, elastic properties, hardness and relevant electronic structure of Ni–P compounds (Ni3P, Ni12P5, Ni2P, Ni5P4, NiP, NiP2 and NiP3) was carried out using first principles calculations. The calculated results show that the Ni–P compounds have strong hardness, ranging from 7.80–14.54 GPa. Also, the hardness values gradually increase with the P content. Electronic structure analysis shows that the strong Ni–P and part of P–P hybrid orbitals play important roles in the hardness of these compounds. The calculated elastic constants indicated that the Ni3P, Ni12P5 and NiP2 phases are significantly anisotropic, the NiP and Ni2P exhibit some anisotropy, while the Ni5P4 and NiP3 show a relatively isotropic character. At last, the properties of these Ni–P compounds including lattice constants, thermodynamic stability, elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν have been calculated.

Geometry, chemical reactivity and Raman spectra of gold clusters

AbstractStructures, stability, and chemical reactivity of Aun (n = 2-10) clusters are investigated using density functional theory (DFT). We have studied the reactivity parameters of the clusters in terms of relevant electronic structure principles. It is observed that stability and properties are strongly dependent on the cluster size. Clusters with an even number of atoms are found to be energetically and chemically more stable than odd-numbered clusters. Electronic structure of clusters has been investigated using partial density of states (PDOS). PDOS analysis clearly shows that energy states of highest occupied molecular orbital and lowest unoccupied molecular orbital are predominantly contributed by s orbital. From time-dependent DFT calculations, it is shown that absorption spectra of even-numbered clusters are more intense and are observed at lower wavelength region than the odd-sized gold clusters.

Singlet fission in linear chains of molecules.

We develop a model configuration interaction Hamiltonian to study the electronic structure of a chain of molecules undergoing singlet fission. We first consider models for dimer and trimer and then we use a matrix partitioning technique to build models of arbitrary size able to describe the relevant electronic structure for singlet fission in linear aggregates. We find that the multi-excitonic state (ME) is stabilized at short inter-monomer distance and the extent of this stabilization depends upon the size of orbital coupling between neighboring monomers. We also find that the coupling between ME states located on different molecules is extremely small leading to bandwidths in the order of ∼10 meV. This observation suggests that multi-exciton states are extremely localized by electron-phonon coupling and that singlet fission involves the transition between a relatively delocalized Frenkel exciton and a strongly localized multi-exciton state. We adopt the methodology commonly used to study non-radiative transitions to describe the singlet fission dynamics in these aggregates and we discuss the limit of validity of the approach. The results indicate that the phenomenology of singlet fission in molecular crystals is different in many important ways from what is observed in isolated dimers.

Some Ruthenium Derivatives of Penta-1,4-diyn-3-one

The reaction between Ru(C≡CH)(dppe)Cp* (1) and oxalyl chloride affords ({Ru(dppe)Cp*}C≡C)2CO (2) in 72% yield. Methylation (MeOTf) of 2 occurs first on the carbonyl oxygen, affording [({Ru(dppe)Cp*}C≡C)2C(OMe)]OTf ([3]OTf). A second methylation of [3]+ on the alkynyl Cβ proceeds slowly, affording [{Cp*(dppe)Ru}CCMeC(OMe)CC{Ru(dppe)Cp*}][OTf]2 ([4][OTf]2), whereas protonation of [3]+ occurs readily to give crystallographically characterized [{Cp*(dppe)Ru}CCHC(OMe)CC{Ru(dppe)Cp*}][OTf]2 ([5][OTf]2). The molecular structures of [3]OTf and [5][OTf]2 suggest that polarization by the CO group results in significant contributions from the alkynyl-allenylidene or alkynyl-carbyne mesomers, respectively. Reaction of 2 in refluxing MeOH containing [NH4]PF6 results in partial methanolysis to give Ru{C≡CC(O)CH═CH(OMe)}(dppe)Cp* (6). Knövenagel condensation of 2 with CH2(CN)2 affords {[Ru(dppe)Cp*]C≡C}2C═C(CN)2 (7). The related asymmetric complex {Cp*(dppe)Ru}C≡C[C═C(CN)2]C≡CC≡C{Ru(dppe)Cp*} (8) was obtained from the reaction between Ru{C≡CC(CN)═C(CN)2}(dppe)Cp* and lithiated Ru(C≡CC≡CH)(dppe)Cp*. Single-crystal structural determinations of 2, [3]OTf, [5][OTf]2, 6, 7, and 8 are reported, together with a supporting computational study of relevant electronic structures.

Hole mediated ferromagnetism in Cu-doped ZnO thin films on GaAs substrate

We studied the ferromagnetic properties and the relevant electronic structure of hole-doped ZnO:Cu films, using the element specific techniques of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). Hole-doping is achieved through As diffusion from the GaAs substrate to the deposited ZnO:Cu films, assisted by thermal annealing. The As-diffusion is probed with the help of XAS collected at the As K-edge which shows enhanced signature of diffusion in the annealed samples. Cu charge state and the introduction of holes due to the As doping in ZnO:Cu films are investigated by the Cu L3,2-edge spectra. XMCD and magnetic measurements show that the magnetic moments originate from the doped Cu ions and that the magnetization is enhanced by the increase in As diffusion and hole doping which suggests a hole-mediated exchange interaction among the doped magnetic moments.

Communication: Hydration structure and polarization of heavy alkali ions: A first principles molecular dynamics study of Rb+ and Cs+

Hydration structure and polarization of Rb(+) and Cs(+) in liquid water at ambient conditions were studied by first principles molecular dynamics. Our systematic analysis of the relevant electronic structures, based on maximally localized Wannier functions, revealed that the dipole moment of H(2)O molecules in the first solvation shell of the ions slightly increases with increasing the atomic number. We also found that the polarization of heavy alkali ions, particularly Cs(+), tends to stabilize a peculiar asymmetric hydration structure with relevant consequences in the extraction of the harmful (137)Cs resulting from nuclear wastes.

Extrapolating potential energy surfaces by scaling electron correlation: Isomerization of bicyclobutane to butadiene

The recently proposed potential energy surface (PES) extrapolation scheme, which predicts smooth molecular PESs corresponding to larger basis sets from the relatively inexpensive calculations using smaller basis sets by scaling electron correlation energies [A. J. C. Varandas and P. Piecuch, Chem. Phys. Lett. 430, 448 (2006)], is applied to the PESs associated with the conrotatory and disrotatory isomerization pathways of bicyclo[1.1.0]butane to buta-1,3-diene. The relevant electronic structure calculations are performed using the completely renormalized coupled-cluster method with singly and doubly excited clusters and a noniterative treatment of connected triply excited clusters, termed CR-CC(2,3), which is known to provide a highly accurate description of chemical reaction profiles involving biradical transition states and intermediates. A comparison with the explicit CR-CC(2,3) calculations using the large correlation-consistent basis set of the cc-pVQZ quality shows that the cc-pVQZ PESs obtained by the extrapolation from the smaller basis set calculations employing the cc-pVDZ and cc-pVTZ basis sets are practically identical, to within fractions of a millihartree, to the true cc-pVQZ PESs. It is also demonstrated that one can use a similar extrapolation procedure to accurately predict the complete basis set (CBS) limits of the calculated PESs from the results of smaller basis set calculations at a fraction of the effort required by the conventional pointwise CBS extrapolations.

Hydration of alkali ions from first principles molecular dynamics revisited

Structural and dynamical properties of the hydration of Li(+), Na(+), and K(+) in liquid water at ambient conditions were studied by first principles molecular dynamics. Our simulations successfully captured the different hydration behavior shown by the three alkali ions as observed in experiments. The present analyses of the dependence of the self-diffusion coefficient and rotational correlation time of water on the ion concentration suggest that Li(+) (K(+)) is certainly categorized as a structure maker (breaker), whereas Na(+) acts as a weak structure breaker. An analysis of the relevant electronic structures, based on maximally localized Wannier functions, revealed that the dipole moment of H(2)O molecules in the first solvation shell of Na(+) and K(+) decreases by about 0.1 D compared to that in the bulk, due to a contraction of the oxygen lone pair orbital pointing toward the metal ion.

Characterization of the molecular iodine electronic wave functions and potential energy curves through hyperfine interactions in the B0+_u(3Pi_u) state

We present a high-resolution analysis of the six electronic states that share the same dissociation limit with the second excited electronic state B in molecular iodine. These six states are coupled to the B state via hyperfine interactions. The four hyperfine parameters, C_B, delta_B, d_B, and eqQ_B, are calculated with the available potential energy curves and wave functions constructed from the separated-atom basis set. We obtain a maximum separation of the respective contributions from all six electronic states and compare each individual contribution with high-precision spectroscopic data, providing an independent verification of the relevant electronic structure.

On the evaluation of nonadiabatic coupling matrix elements for MCSCF/CI wave functions. IV. Second derivative terms using analytic gradient methods

A recently proposed methodology for determining second derivative nonadiabatic coupling matrix elements h(J,I,Rα,R) ≡〈ΨJ(r;R)‖(∂2/∂R2α )ΨI(r;R)〉r based on analytic gradient methods is implemented and discussed. Here r denotes the electronic coordinates, R the nuclear coordinates, and the ΨJ (r;R) are eigenfunctions of the nonrelativistic Born–Oppenheimer Hamiltonian at the state averaged MCSCF/CI level. The region of a conical intersection of the 1,2 2A′ potential energy surfaces of the Li–H2 system is considered in order to illustrate the potential of this approach. The relation between h(J,I,Rα,R) and the first derivative matrix elements g(J,I,Rα,R) ≡〈ΨJ(r;R)‖(∂/∂Rα)ΨI (r;R)〉r is considered and the role of symmetry discussed. The h(J,I,Rα,R) are analyzed in terms of contributions from molecular orbital and CI coefficient derivatives and the importance of the various nuclear degree of freedom, Rα, is considered. It is concluded that for the case considered a flexible multiconfiguration wave function is desirable for characterizing h(J,I,Rα,R). This methodology complements recent advances in treating nonadiabatic processes for diatomic and triatomic systems starting with adiabatic states, including the work of Mead, Truhlar, and co-workers on conical (Jahn–Teller) intersections in X3 systems, by providing an essential computational step for the ab initio characterization the relevant electronic structure parameters.