Structure and stability of AgXen Z({\sf n=1}–3, {\sf Z=-1}, 0, +1) clusters. Theoretical insights

The structure and stability of AgXe_n ^Z(n=1–3, Z=-1, 0, +1) cluster series at CCSD(T) theoretical level have been investigated. It is shown that the cations are more stable and have more compact geometries than the anions and neutrals. The role of the interaction was explained using the natural bond orbital (NBO) analysis.     

38≤Z≤42类钴离子n=3,△n=0跃迁的理论计算

用多组态自洽场方法,结合作提出的半经验拟合公式,首先对３８≤Ｚ≤４２类钴离子３ｐ＾６３ｄ＾９,３ｐ＾５３ｄ＾１０,３ｐ＾６３ｄ＾８４ｐ组态的能级进行计算,然后根据能级值算出相应的电偶极跃迁的谱线波长,并给出各谱线的ＨＦＲ振子强度。     

Structure and chemical valence study of Sr_(n+1)Ru_nO_(3n+1)(n= 1, 2, ∞) series

Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Sr n+1RunO3n+1(n = 1, 2, ∞) are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Sr n+1RunO3n+1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn+1RunO3n+1(n = 1, 2, ∞).     

Observation of Δn=1 dielectronic recombination resonances of boronlike argon

We report here an observation ofn=1 dielectronic recombination resonances of boron-like argon in the energy region 140–195 eV. With the cooler's electron beam as a target, a resolution of approximately 0.6 eV FWHM was obtained in the observed energy range. The energies of the doubly excited states were estimated with a Hartree-Fock calculation, which indicates that the observed resonances are from Ar¹³⁺(1s²2s²2p) to Ar¹²⁺(1s²2s²3l3l) and Ar¹²⁺(1s²2s2p3l3l) transitions.     

The excitation energies and term energies of the excited states 1s2ns (n=3,4,5) and 1s2nf (n=4,5) of lithium-like systems of Z=11－20

In this paper, the full-core plus correlation (FCPC) and the Ritz method is extended to calculate the non-relativistic energies of 1s^2ns (n=3,4,5) and 1s^2nf (n=4,5) states and the wavefunctions of the lithium-like systems from Z=11－20. The mass-polarization and the relativistic correction including the kinetic-energy correction, the Darwin term, the electron－electron contact term, and the orbit－orbit interaction are evaluated perturbatively as the first-order correction. The contribution from quantum electrodynamic is also included by using the effective nuclear charge formula. The excited energies, the term-energy and fine structure, are given and compared with the other theoretical calculation and experimental results. It is shown that the correlative wave in the FCPC method embodies well the strong correlation between the 1s^2 core and the valence electron.     

Structures,thermochemistry, and electron affinities of the disilicon fluorides,Si2F n /Si2F− n (n = 1–6)

A systematic investigation of Si₂F_n/Si₂F^? _n systems is carried out with five density functional (DFT) methods in conjunction with DZP++ basis sets. For each system, various structures, including minima, transition states, and energetically low lying saddle points, are optimized. The geometries and the relative energies are discussed and compared. Three kinds of electron affinity and dissociation energy pertaining to the global minimum for each compound are reported. The theoretical predictions are in good agreement with the limited experimental results. The zero-point vibrational energy (ZPVE) corrected adiabatic electron affinities (EA_ad) are predicted as 1.97 (Si₂F), 1.92 (Si₂F₂), 2.39 (Si₂F₃), 2.02 (Si₂F₄), 2.68 (Si₂F₅), and 0.73 (Si₂F₆)eV by the BHLYP method, which is considered to be the most reliable method in the present study for predicting the EAs. These theoretical predictions are quite different from those for the analogous silicon hydrides and fluorocarbons. For example, both Si₂F₂ and its anions have vinylidene-like (Si-SiF₂) global minima. The anion SiSi bond distance is about 0.1 Å shorter than that for the Si—SiF₂ neutral. Both Si₂F₃ and its anion have carbyne-like (Si-SiF₃) global minima, with the anion SiSi distance about 0.05 Å shorter. Both Si₂F₄ and its anion have carbene-like (FSi-SiF₃) global minima, again with the negative ion SiSi distance ～0.05 Å shorter. Surprisingly, doubly bridged structures of Si₂F₄ are energetically competitive. For the ethyl-radical-like Si₂F₅, the expected longer SiSi distance (by 0.13 Å) for the anion is predicted. Whereas Si₂H₄, C₂F₄, Si₂H₆, and C₂F₆ do not have significant electron affinities, Si₂F₄ and Si₂F₆ do bind an electron. However, the unexpected Si₂F^? ₆ species has a significantly longer SiSi distance (by 0.15 Å) than that of neutral Si₂F₆.     

38≤Z≤42类钴离子n =3、Δn=0跃迁的理论计算

用多组态自洽场方法,结合作者提出的半经验拟合公式,首先对38≤Z≤42类钴离子3p63d9,3p53d10,3p63d84p组态的能级进行计算,然后根据能级值算出相应的电偶极跃迁的谱线波长,并给出各谱线的HFR振子强度。     

Structures and energetics of BenGen (n = 1–5) and Be2nGen (n = 1–4) clusters

Cluster geometries and energies of Be_nGe_n (n = 1–5) and Be_2nGe_n (n = 1–4) have been examined in theoretical electronic structure calculations. Structure optimisations were carried out using DFT B3LYP/6-31G(2df) and the energies of the optimum geometries were ordered in QCISD(T) calculations. Be and Ge bond to each other and to other atoms of their own kind, creating a great variety of low-energy clusters in a variety of structural types. Comparisons of the germanide clusters with previously explored silicide and carbide structures reveal some structural similarities, but the germanides have much more in common with the beryllium silicides than with the carbides. However, germanide clusters show a greater tendency to form cage-like structures with potential in technological applications.     

A systematic investigation of the geometries,electronic and magnetic properties of AlnAsq (q = −1, 0, +1; n = 1–16) clusters: a DFT calculation

The geometries, electronic and magnetic properties of Al_nAs^q (q = ?1, 0, +1; n = 1–16) clusters have been investigated systematically by using an unbiased CALYPSO structure searching method and density functional theory. The lowest energy structures show that the As atom prefers to occupy the peripheral position of Al_n+1 clusters instead of the endohedral position. For cationic and neutral clusters, the structural transition from bilayer-like structure to cage-like structure is observed at cluster size n = 12, while it occurs at n = 13 for anionic clusters. The calculated detachment energies (DEs), ionisation potentials (IPs) and electronic affinities (EAs) are consistent with the available experimental and theoretical results for small clusters, indicating that the calculated lowest energy structures are reliable. Furthermore, the DE, EA and IP values for cluster size n ≥ 6 are successfully predicted. A stability analysis shows that Al₅As and Al₁₂As⁺ clusters have relatively large HOMO–LUMO energy gaps, corresponding to the magic numbers of 20 and 40 valence electrons, respectively.     

Density functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin （n - 1-8） clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital （NBO） are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6 clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.     

Theoretical studies on the structures and absorption spectra of–C n R2n+1(R = H,F; n = 1, 2) substituted 5-(2-pyridyl) pyrazolate boron complexes

The molecular structures, electronic structures and absorption characters of–CH₃,–C₂H₅,–CF₃,–C₂F₅ substituted 5-(2-pyridyl) pyrazolate boron complexes were presented by density functional theory (DFT). The ground state structures of the title complexes were optimised at B3LYP/6-31G* level. In addition, a time dependent density functional theory (TD-DFT) method is applied to investigate the properties of absorption spectra and electronic transition mechanism which were based on the ground state geometries. The results show that the chemical bond formed between nitrogen in the pyridyl ring and boron can be attributed to coordination effect. The boron centre has a typical tetrahedral geometry with the adjacent atoms. The calculated absorption wavelengths for–CF₃,–C₂F₅ substituted 5-(2-pyridyl) pyrazolate boron complexes are in good agreement with the experimental data.     

First-Principles Study of Geometries,Stabilities and Electronic Properties of Ca2Sin （n=1-11） Clusters

The equilibrium geometries, relative stabilities, and electronic properties of Ca2Sin （n = 1-11） clusters have been systematically investigated by using the density function theory at the 6-311G （d） level The optimized geometries indicate that the most stable isomers have three-dimensional structures for n = 3-11. The electronic properties of Ca2 Sin （n = 1-11） dusters axe obtained through the analysis of the natural charge population, natural electron configuration, vertical ionization potential, and vertical electron affinity. The results show that the charges in corresponding Ca2Sin clusters transfer from the Ca atoms to the Sin host. Based on the obtained lowest-energy geometries, the size dependence of cluster properties, such as averaged binding energies, fragmentation energies, second-order energy differences, HOMO- LUMO gaps and chemical hardness, are deeply discussed.     

重费米子化合物 CemMnIn3m+2n(m = 1, 2, 3; n = 0, 1, 2; M = Co,Rh,Ir,Pt 及Pd) 的角分辨光电子能谱研究

重费米子材料以其新奇多变的宏观性质,复杂而难以理解的微观物理过程而受到广泛的关注,长期是凝聚态物理研究的重点。角分辨光电子能谱作为一种能够直接探测材料电子结构的实验手段,随着近年来实验技术的高度发展,能量和动量分辨率得到了极大的提高,能够有力地探测到强关联材料中更加精细的电子结构。使用角分辨光电子能谱探测重费米子材料的电子结构,为理解其各种物理过程提供强有力的实验证据,进而推进重费米子理论的发展。本文回顾 Ce 基重费米子材料 CemMnIn3m+2n (m = 1; 2; 3;n = 0; 1; 2;M =Co, Rh, Ir, Pt, Pd) 系列化合物的角分辨光电子能谱研究,包括电子结构的维度、近藤共振、f 电子与导带电子的杂化和电子结构随温度的变化等。     

161Dy Mössbauer study of the endohedral metallofullerenes Dy@C n (n = 80, 82, 84)

Mössbauer studies of Dy@C _n (n = 80, 82, 84) metallofullerenes were performed at 4.2, 9.6 and 78 K with the ¹⁶¹Dy (25.6 keV) resonance. The observed spectra consist of two subspectra splitted by magnetic hyperfine fields near to the full moment value of trivalent Dy. Paramagnetic relaxation is observed even at 4.2 K. The observed isomer shift is consistent with the Dy³⁺ state and indicates a full charge transfer to the fullerene cage.     

Single-phase Bi2+x(Ca,Sr) n+1 Cu n O2n+4+δ, n = 0, 1, 2, 3 AND ∞, and some substitutional DERIVATIVES

The preparation, structure and properties of five members of the homologous series Bi_2+x(Ca,Sr) _n+1 Cu _n O_2n+4+δ are discussed, namely for n = 0, 1, 2, 3 and ∞. The two end members are insulating phases with a fixed oxygen stoichiometry but the members n = 1, 2 and 3 are superconducting phases with T_c depending on the calcium to strontium ratio and on oxygen stoichiometry as determined by annealing temperature and oxygen partial pressure. Maximum zero resistance T_c 's obtained are n = 1: 76 K, n = 2: 91 K and n = 3: 106 K. The effects of Pb-substitution in n = 2 and n = 3 are discussed with particular reference to the stabilisation of the latter phase. Rare-earth substitution is shown to raise T_c for n = 2 to at least 101 K without the introduction of the n = 3 phase.     

Synthesis and characterization of layered perovskite oxides (La, Sr) n + 1(Ti, Cr) n O3n + 1 (n = 1, 2)

We report here the synthesis of layered perovskite oxides of the composition La_0.5Sr_1.5Ti_0.5Cr_0.5O₄ and LaSr₂TiCrO₇ by conventional solid-state reaction method. Results of XRD analysis show that the phases crystallize with tetragonal unit cell in the space group I4/mmm. Both phases behave as insulators and the linearity of log ρ versus T ^?1/4 plot in the temperature range 150–350 K suggests that the electronic conduction occurs by Mott’s variable range hopping mechanism. The antiferromagnetic interactions observed for the samples arise from Cr³⁺–O–Cr³⁺ superexchange interaction.     

Geometries,stabilities, electronic and magnetic properties of small PdnIr (n = 1–8) clusters from first-principles calculations

The geometrical structures, relative stabilities, electronic and magnetic properties of small Pd_nIr (n = 1–8) clusters have been systematically investigated using density functional theory at the B3PW91 level. The optimised geometries show that the lowest-energy structures of Pd_nIr clusters prefer a three-dimensional configuration. The relative stability of these clusters was examined by analysis of the binding energies per atom, fragmentation energies, the second-order difference of energies and the HOMO–LUMO energy gaps as a function of cluster size. The obtained results exhibit that the Pd₂Ir, Pd₃Ir and Pd₅Ir clusters are more stable than their neighbouring clusters. The energy gap of the Pd₂Ir cluster is the largest of all the clusters (2.258 eV). In addition, the charge transfers, vertical ionisation potentials, vertical electron affinities and chemical hardness were calculated and discussed. The magnetism calculations indicate that the total magnetic moment of Pd_nIr clusters is mainly localised on the iridium atom for Pd_1–6Ir clusters. Meanwhile, the 5d orbital plays the key role in the magnetic moment of the iridium atom.     

Observation and Simulation of n=1 Reversed Shear Alfvén Eigenmode on the HL-2A Tokamak

A branch of high-frequency Alfvénic modes is observed on the HL-2 A tokamak. The electromagnetic mode can be driven unstably in the plasma with an off-axis neutral beam heating. Its mode frequency keeps almost unchanged or presents a slow-sweeping behavior, depending on the detail current evolution. The poloidal and toroidal mode numbers are m/n = 1/1. The mode has a quite short duration(≤20 ms) and usually appears 5–10 ms after the neutral beam being injected into the plasma. Hybrid simulations...