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The geometric, optical, and magnetic properties of the M@Sn12 clusters (M=Ti, V, Cr, Mn, Fe, Co, Ni) are studied using the relativistic density-functional method. The geometric optimization shows that the ground states of these clusters are probably very close to the Ih structure. Our calculations demonstrate that the optical gaps of the M@Sn12 can be tuned from infrared to green, and the magnetic moments of them vary from 2 μB to 5 μB by doping d transition metal atoms into Sn12 cage, suggesting that M@Sn12 could be a new class of potential nanomaterials with tunable magnetic and optical properties. [ABSTRACT FROM AUTHOR]

The geometric and electronic properties of the titanium carbide TiC5 cluster in its neutral and anionic charge states have been investigated using density functional theory (DFT) at the B3LYP level. The nonplanar six-membered ring-type or “butterflylike” structures are found to be the equilibrium geometric structures of TiC5 and TiC5-. Time-dependent DFT is used in the calculation of the excited states. The theoretical assignment at the B3LYP level for the features in the photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

The geometric and electronic structures of metal-substituted fullerene C59Sm and exohedral fullerenes C60Sm are studied using the density-functional theory. The geometric optimization shows that the replacement of a C atom with a Sm in C60 yields a stable substitutionally doped fullerene C59Sm, and among the five possible optimized geometries for C60Sm, the most favorable exohedral sites are above the center of a hexagon and a pentagon ring. The calculations for electronic structures show that the magnetic moment of Sm is preserved for all the stable structures as tiny hybridization takes place between the orbitals of the Sm atom and those of their neighboring carbons. Because of the small energy gaps and the half occupation of the highest occupied molecular orbitals, all the stable C60Sm isomers are inferred to be conductors. [ABSTRACT FROM AUTHOR]

Investigates the electrocrystallization of copper (Cu) phthalocyaninato (pc). Metallic conductivity of porphyritic compound; Molecular structure of Cu pc ring; Identification of the magnetic coupling energy of Cu spins.

The generalized gradient approximation based on density functional theory is used to analyze the geometric and electronic properties of Si@C74. It is found that among the five possible optimized geometries of Si@C74, the most favorable endohedral site of Si atom is under the center of a pentagon ring on the σh plane, i.e., Si@C74-5, which is different from the center stable site for Si in C74 calculated by the semiempirical molecular orbital calculations and molecular mechanics calculations, and it is also different from the stable site, i.e., under a [6, 6] bond along the C2 axis on the σh plane in C74 for metal atoms Ba, Ca, and Eu. The deformation charge density on the σh plane reveals that the Si–C bonds in Si@C74-5 have covalent character, while the Mulliken charge analysis together with a longer Si–C bond length reveals that the Si–C bonds in Si@C74-5 have ionic character. Therefore, we infer that Si–C bonds in Si@C74-5 contain both covalent and ionic characters. [ABSTRACT FROM AUTHOR]

In spite of decades of research, a fundamental understanding of the unusual magnetic behavior of small Mn clusters remains a challenge. Experiments show that Mn2 is antiferromagnetic while small clusters containing up to five Mn atoms are ferromagnetic with magnetic moments of 5 μB/atom and become ferrimagnetic as they grow further. Theoretical studies based on density functional theory (DFT), however, find Mn2 to be ferromagnetic, with ferrimagnetic order setting in at different sizes that depend upon the computational methods used. While quantum chemical techniques correctly account for the antiferromagnetic ground state of Mn2, they are computationally too demanding to treat larger clusters, making it difficult to understand the evolution of magnetism. These studies clearly point to the importance of correlation and the need to find ways to treat it effectively for larger clusters and nanostructures. Here, we show that the DFT+U method can be used to account for strong correlation. We determine the on-site Coulomb correlation, Hubbard U self-consistently by using the linear response theory and study its effect on the magnetic coupling of Mn clusters containing up to five atoms. With a calculated U value of 4.8 eV, we show that the ground state of Mn2 is antiferromagnetic with a Mn-Mn distance of 3.34 Å, which agrees well with the electron spin resonance experiment. Equally important, we show that on-site Coulomb correlation also plays an important role in the evolution of magnetic coupling in larger clusters, as the results differ significantly from standard DFT calculations. We conclude that for a proper understanding of magnetism of Mn nanostructures (clusters, chains, and layers) one must take into account the effect of strong correlation. [ABSTRACT FROM AUTHOR]

Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.09 × 10-1 cm2 V-1 s-1 which can be applied in the molecular wire. The findings also show that our theoretical model can be regarded as a promising candidate for screening DNA- and RNA-based molecular electronic devices. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive study of (TiO2)n (n=1–3) clusters on their structures, vertical electron affinities (VEA) and adiabatic electron affinities (AEA), and excited states that are further correlated with experimental photoelectron spectra (PES). Local density functional and time-dependent density functional methods (TTDFT) with 6–31G(d) basis set are used. For (TiO2)n with n=1 and 3, the ground-state geometries are found to have C2v and Cs structures, respectively, in both neutral and anionic charge states. For neutral (TiO2)2, the most stable structure corresponds to a C2h conformation. For anionic (TiO2)2-, two isomers with C2h and C2v symmetries are identified to be nearly isoenergetic. This conclusion is supported by reoptimization at CCSD/6–31G(d) level and single-point calculation at CCSD(T)/6-311+G(d) level. Hence, they are competitive candidates for the ground-state structure of (TiO2)2-. For TiO2 and (TiO2)3, the calculated VEA and AEA values agree well with the experimental data. For (TiO2)2, the VEA and AEA obtained with the C2v structure agree well with the experimental data while those with the C2h structure do not. The subsequent assignment of PES indicates that it is the C2v isomer of (TiO2)2- that represents the structure from which the photoexcitation in experimental PES takes place. TDDFT is used to determine the excited states of (TiO2)n (n=1–3) and the calculated excitation energies are in good agreement with PES experiment. [ABSTRACT FROM AUTHOR]

Ferroelectrics have many significant applications in electric devices, such as capacitor or random-access memory, tuning the efficiency of solar cell. Although atomic-thick ferroelectrics are the necessary components for high-density electric devices or nanoscale devices, the development of such materials still faces a big challenge because of the limitation of intrinsic mechanism. Here, we reported that in-plane atomic-thick ferroelectricity can be induced by vertical electric field in phosphorene nanoribbons (PNRs). Through symmetry arguments, we predicted that ferroelectric direction is perpendicular to the direction of external electric field and lies in the plane. Further confirmed by the comprehensive first-principles calculations, we showed that such ferroelectricity is induced by the electron-polarization, which is different from the structural distortion in traditional ferroelectrics and the recent experimental discovery of in-plane atomic-thick ferroelectrics (Science 2016, 353, 274). Moreover, we found that the value of electronic polarization in bilayer is much larger than that in monolayer. Our results show that electron-polarization ferroelectricity maybe the most promising candidate for atomic-thick ferroelectrics. [ABSTRACT FROM AUTHOR]

High-temperature ferromagnetic two-dimensional (2D) materials with flat surfaces have been a long-sought goal due to their potential in spintronics applications. Through comprehensive first-principles calculations, we show that the recently synthesized MoN2 monolayer is such a material; it is ferromagnetic with a Curie temperature of nearly 420 K, which is higher than that of any flat 2D magnetic materials studied to date. This novel property, made possible by the electron-deficient nitrogen ions, render transition-metal dinitrides monolayers with unique electronic properties which can be switched from the ferromagnetic metals in MoN2, ZrN2, and TcN2 to half-metallic ones in YN2. Transition-metal dinitrides monolayers may, therefore, serve as good candidates for spintronics devices. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of Cu2ZnSiS4, Cu2ZnSiSe4 and Cu2ZnSiTe4 in kesterite and stannite structures are systematically studied using first-principles calculations. Crystal field splitting, optical transitions, p-d bonding, and anti-bonding overlapping are analyzed. The physical and chemical trends in these properties are investigated with respect to the crystal structure and anion atomic number. The optical spectra, such as dielectric function, refractive index, reflectivity and absorption coefficient are explored in a broad range of energy. A good agreement between the calculated results and experimental data is obtained. [ABSTRACT FROM AUTHOR]

Based on density functional theory and the first principles molecular dynamics simulations, a threedimensional B-doped graphene-interconnected framework has been constructed that shows good thermal stability even after metal loading. The average binding energy of adsorbed Li atoms on the proposed material (2.64 eV) is considerably larger than the cohesive energy per atom of bulk Li metal (1.60 eV). This value is ideal for atomically dispersed Li doping in experiments. From grand canonical Monte Carlo simulations, high hydrogen storage capacities of 5.9 wt% and 52.6 g/L in the Li-decorated material are attained at 298 K and 100 bars. [ABSTRACT FROM AUTHOR]

By numerically solving the three dimensional time-dependent Schrödinger equation, we explore the high-order harmonic and attosecond pulse generation of He atoms exposed to a special three-color field. An ultrabroad supercontinuum with a bandwidth of 887 eV has been attained, supporting an isolated 4 as pulse straightforwardly by Fourier transforming. Utilizing available intense infrared femtosecond laser resource within the nonrelativistic regime, the produced laser pulse is near to zeptosecond region. Remarkably, the harmonic conversion efficiency is enhanced in terms of the double-plateau structure of the harmonic spectra, yielding high-intensity atto-second pulses with alternative plateau. [ABSTRACT FROM AUTHOR]

The unprecedented applications of two-dimensional (2D) atomic sheets in spintronics are formidably hindered by the lack of ordered spin structures. Here we present first-principles calculations demonstrating that the recently synthesized dimethylmethylene-bridged triphenylamine (DTPA) porous sheet is a ferromagnetic half-metal and that the size of the band gap in the semiconducting channel is roughly 1 eV, which makes the DTPA sheet an ideal candidate for a spin-selective conductor. In addition, the robust half-metallicity of the 2D DTPA sheet under external strain increases the possibility of applications in nanoelectric devices. In view of the most recent experimental progress on controlled synthesis, organic porous sheets pave a practical way to achieve new spintronics. [ABSTRACT FROM AUTHOR]

The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems. On the basis of first-principles calculations, we reveal that a charged CrBr3 monolayer exhibits in-plane multiferroicity, which is ensured by the combination of orbital and charge ordering as realized by the asymmetric Jahn-Teller distortions of octahedral Cr-Br6 units. As an example, we further show that (CrBr3)2Li is a ferromagnetic ferroelectric multiferroic. The explored phenomena and mechanism of multiferroics in this 2D system not only are useful for fundamental research in multiferroics but also enable a wide range of applications in nanodevices. [ABSTRACT FROM AUTHOR]

The quantum anomalous Hall (QAH) effect is a novel topological spintronic phenomenon arising from inherent magnetization and spin-orbit coupling. Various theoretical and experimental efforts have been devoted in search of intrinsic QAH insulators. However, up to now, it has only been observed in Cr or V doped (Bi,Sb)2Te3 film in experiments with very low working temperature. Based on the successful synthesis of transition metal halides, we use first-principles calculations to predict that the RuI3 monolayer is an intrinsic ferromagnetic QAH insulator with a topologically nontrivial global band gap of 11 meV. This topologically nontrivial band gap at the Fermi level is due to its crystal symmetry, thus the QAH effect is robust. Its Curie temperature, estimated to be ~360K using Monte Carlo simulation, is above room temperature and higher than most two-dimensional ferromagnetic thin films. The inclusion of Hubbard U in the Ru-d electrons does not affect this result. We also discuss the manipulation of its exchange energy and nontrivial band gap by applying in-plane strain. Our work adds an experimentally feasible member to the QAH insulator family, which is expected to have broad applications in nanoelectronics and spintronics. [ABSTRACT FROM AUTHOR]