C4v Symmetry Crystal Field and Ground State Wavefunction of the VO^2＋ Ion

The spin-Hamiltonian parameters obtained from EPR studies of the VO^2＋ ion in different diamagnetic host lattices are used to estimate the ground state wavefunctions. These are of dxy type with admixture of the excited states dx2-y2, dyz and dxz. The hyperfine interaction parameter and Fermi contact term for the VO^2＋ doped crystals are determined using the coefficients of the ground state. The various parameters are correlated to the ligand properties of the complexes.     

Structure and stability of various states of the EuC and EuC2 molecules

B3LYP level density functional theory （DFT） and multiconfiguration self-consistent-field （MCSCF） level ab initio method calculations have been performed on the basis of relativistic effective core potentials to investigate the nature of EuC and EuC2 molecules. The computed results indicate that the ground states of EuC and EuC2 are ^12∑^＋ and SA2, respectively. Dissociation potential energy curves of the low-lying electronic states of EuC have been calculated using the MCSCF method, and the same level calculation on EuC2 indicates that the dissociation energy of EuC2 of ground state compares well with the available experimental data. The bond characteristic is also discussed using Mulliken populations.     

Studies on Electronic Structure and Magnetic Properties of an Organic Magnet with Metallic Mn^2＋ and Cu^2＋ Ions

The electronic structure and the magnetic properties of the non-pure organic ferromagnetic compound MnCu(pbaOH)(H2O)3 with pbaOH=2-hydroxy-1, 3-propylenebis (oxamato) are studied by using the density-functional theory with local-spin-density approximation. The density of states, total energy, and the spin magnetic moment are calculated. The calculations reveal that the compound MnCu(pbaOH)(H2O)3 has a stable metal-ferromagnetic ground state, and the spin magnetic moment per molecule is 2.208 μa, and the spin magnetic moment is mainly from Mn ionand Cu ion. An antiferromagnetic order is expected and the antiferromagnetic exchange interaction of d-electrons of Cu and Mn passes through the antiferromagnetic interaction between the adjacent O, 0, and N atoms along the path linking the atoms Cu and Mn.     

Electronic structure of La (0001) thin films on W (110) studied by photoemission spectroscopy and first principle calculations

Surface states that have a dz2 symmetry around the center of the surface Brillouin zone(BZ)have been regarded common in closely-packed surfaces of rare-earth metals.In this work,we report the electronic structure of dhcp La(0001)thin films by ultrahigh energy resolution angle-resolved photoemission spectroscopy(ARPES)and first principle calculations.Our first principle analysis is based on the many-body approach,therefore,density function theory(DFT)combined with dynamic mean-field theory(DMFT).The experimentally observed Fermi surface topology and band structure close to the Fermi energy qualitatively agree with first principle calculations when using a renormalization factor of between 2 and 3 for the DFT bands.Photon energy dependent ARPES measurements revealed clear kZ dependence for the hole-like band around the BZ center,previously regarded as a surface state.The obtained ARPES results and theoretical calculations suggest that the major bands of dhcp La(0001)near the Fermi level originate from the bulk La 5d orbits as opposed to originating from the surface states.     

Structural,electronic,and magnetic properties of vanadium atom-adsorbed MoSe_2 monolayer

Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe_2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearestneighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe_2, and the peak of density of states right below the Fermi energy is associated with the V- dz~2 orbital. A single V adatom induces a magnetic moment of 5 μBthat mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition,the crystal field squashes a part of the V-4s electrons into the V-3d orbitals, which enhances the local magnetic moment.The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations(GGA) and GGA+U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic(FM) and antiferromagnetic(AFM) states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA+U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.     

Electronic and Magnetic Properties of Double Perovskite Ca2CrSbO6

First-principles calculations have been performed for the study of the electronic band structure and ferromagnetic properties of double perovskite Ca2CrSbO6. The density of states, total energy, spin magnetic moment, and charge density were calculated and analyzed in details. It is found that Ca2CrSbO6 has a stable ferromagnetic ground state and the spin magnetic moment per molecule is about 2.99#B. The chromium contributes the most in the total magnetic moments. The results indicate that Ca2CrSbO6 is half-metallic.     

Structure and analytical potential energy function for the ground state of the BCx (x=0, －1)

In this paper, the electronic states of the ground states and dissociation limits of BC and BC- are correctly determined based on group theory and atomic and molecular reaction statics. The equilibrium geometries, harmonic frequencies and dissociation energies of the ground state of BC and BC- are calculated by using density function theory and quadratic CI method including single and double substitutions. The analytical potential energy functions of these states have been fitted with Murrell-Sorbie potential energy function from our ab initio calculation results. The spectroscopic data （αe, ωe and ωeχe） of each state is calculated via the relation between analytical potential energy function and spectroscopic data. All the calculations are in good agreement with the experimental data.     

Ab initio study on phase transition and magnetism of BiFeO3 under pressure

In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure of phase transition is reached. The critical pressure for the insulator-metal transition (IMT) is found to be about 50 GPa. A pressure induced crossover of high-spin states and low-spin states is observed close to the IMT pressure in R3c structure. The LSDA+U calculations account well for the mechanism of the IMT and crossover of spin states predicted in recent experiment (Ref.[1]).     

Calculation of scanning tunnelling microscopy images for Kr/graphite system

The scanning-tunnelling-microscopy (STM) images of Kr atoms adsorbed on a monolayer graphite sheet (Kr/graphite system) are calculated using the first-principle total-energy electronic structure calculations within the density functional theory in the local density approximation. The results obtained agree well with the observations. It is found that the optimal site of the adsorbed Kr atom is at the top of the centre of the carbon hexagon, and its equilibrium distance from monolayer graphite surface is about 0.335nm. It is shown that the hybridization of C 2p electronic states (π-electronic states) and Kr 4p and 5s electronic states is the main origin of the Fermi-level local density of state.     

Studies on Electronic Structure and Magnetic Properties of an Organic Magnet with Metallic Mn2+ and Cu2+ Ions

The electronic structure and the magnetic properties of the non-pure organic ferromagnetic compound MnCu(pbaOH)(H2O)3 with pbaOH = 2-hydroxy-1, 3-propylenebis (oxamato) are studied by using the density-functional theory with local-spin-density approximation. The density of states, total energy, and the spin magnetic moment are calculated. The calculations reveal that the compound MnCu(pbaOH)(H20)3 has a stable metal-ferromagnetic ground state, and the spin magnetic moment per molecule is 2.208 μB, and the spin magnetic moment is mainly from Mn ion and Cu ion. An antiferromagnetic order is expected and the antiferromagnetic exchange interaction of d-electrons of Cu and Mn passes through the antiferromagnetic interaction between the adjacent C, O, and N atoms along the path linking the atoms Cu and Mn.     

Tunneling conductance in quantum wire/insulator/dx2 -y2 + idxy mixed wave superconductor junctions

Using the extended Blonder-Tinkham-Klapwijk (BTK) theory, this paper calculates the tunnelling conductance in quantum wire/insulator/dx2-y2 + idxy mixed wave superconductor (q/I/dx2-y2 + idxy) junctions. That is different from the case in d- and p-wave superconductor junctions. When the angle α between a-axis of the dx2-y2 wave superconductor and the interface normal is π/4, there follows a rather distinctive tunnelling conductance. The zero-bias conductance peak (ZBCP) may or may not appear in the tunnelling conductance. Both the interface potential z and the quasi-particle lifetime factor Γ are smaller, there is no ZBCP. Otherwise, the ZBCP will appear. The position of bias conductance peak (BCP) depends strongly on the amplitude ratio of two components for dx2-y2 + idxy mixed wave. The low and narrow ZBCP may coexist with the BCP in the tunnelling conductance. Using those features in the tunnelling conductance of q/I/dx2-y2 + idxy junctions, it can distinguish dx2-y2 + idxy mixed wave superconductor from d- and p-wave one.     

Hf8C12金属碳多面体电子结构的从头计算研究

用赝势从头计算方法研究Hf₈C₁₂多面体．先对T和Td分子构型作几何优化，发现Td对称构型比T构型稳定．利用非限制的Hartre Fock方法及自然键轨道分析研究Td构型的Hf₈C₁₂基团，结果表明：Hf₈C₁₂存在三种自旋不同的基态，这种基态的多样性与成键机制、电子组态和电子能谱分布密切相关．其中S=0时，Hf₈C₁₂主要是由外四面体Hf原子与类乙烯C₂单元形成极性共价键构成．S=1时，6个类乙炔C₂单元吸附在Hf₈金属框架．S=2时，部分C₂中的ｐπ键断裂与Hf原子形成ｄ←ｐπ键．进一步分析发现，Td对称性的结构模型为(Hf₈)^+4.5(C^-0.75₂)₆，在高自旋态下具有铁磁性，电子能级分布及其能隙随自旋态而变化． 关键词：     

Nuclear inelastic scattering studies on a dinuclear iron(II) spin crossover complex

The vibrational properties of the (high-spin)-(high-spin) and the (high-spin)- (low-spin) states of the dinuclear Fe(II) spin crossover complex[{Fe(L-N₄Me₂)}₂(BiBzIm)](ClO₄)₂·2EtCN¹ have been studied by means of nuclear inelastic scattering. At a temperature of 80 K typical low spin marker bands are detected in the region around 400 cm^?1, these bands almost completely disappear after increasing temperature to 190 K. Corresponding density functional theory calculations using the functional B3LYP* and the basis set CEP-31G reproduce the experimental data and thus allow a deeper understanding of the vibrational properties of dinuclear Fe(II) spin crossover complexes.     

Phonon coupled cooperative low-spin 1A1high-spin 5T2 transition in [Fe(phen)2(NCS)2] and [Fe(phen)2(NCSe)2] crystals

Heat capacities of [Fe(phen)₂(NCS)₂] and [Fe(phen)₂(NCSe)₂] were measured between 13⁵ and 375 K. A heat capacity anomaly due to the spin-transition from low-spin ¹A₁ to high-spin π₂ electronic ground state was found at 176·29 K for the SCN-compound and at 231·26 K for the SeCN-compound, respectively. Enthalpy and entropy of transition were determined to be ΔH = 8·60 ± 0·14 kJ mol^?1 and ΔS = 48·78 ± 0·71 J K^?1 mol^?1 for the SCN-compound and ΔH = 11·60 ± 0·44 kJ mol^?1 and ΔS = 51·22 ± 2·33 J K^?1 mol^?1 for the SeCN-compound. To account for much larger value of ΔS compared with the magnetic contribution, we suggest that there is significant coupling between electronic state and phonon system. We also present a phenomenological theory based on heterophase fluctuation. Gross aspects of magnetic, spectroscopic, and thermal behaviors were satisfactorily accounted for by this model. To examine closely the transition process, infrared spectra were recorded as a function of temperature in the range 4000 ? 30 cm^?1. The spectra revealed clearly the coexistence of the ¹A₁, and the ⁵T₂ ground states around T_c.     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd₃(Fe_1-xCo_x)_29-yCr_{y化合物基础上，成功制备出Sm3(Fe1-xCox)29 -yCry化合物，通过x射线衍射和热磁分析对R3(Fe1-x< /sub>Co x)29-yCry 关键词： 3(Fe1-xCox)29-yCry化合物')" href="#">R3(Fe1-xCox)29-yCry化合物 相结构 单轴磁晶各向异性}     

Mössbauer study of CaFeO3 under external high—Pressure

⁵⁷Fe Mössbauer and X-ray diffraction measurements have been performed on a perovskite CaFeO₃ under external high pressure upto 50 GPa at room temperature using a diamond anvil cell. Above 29 GPa the⁵⁷Fe magnetic hyperfine splitting appears superimposing with usual paramagnetic pattern of CaFeO₃. Magnitude of hyperfine field is 16 T and much smaller than 33 T of typical Fe⁴⁺ in SrFeO₃ suggesting a transition from high-spin S=2 to low-spin S=1 state in CaFeO₃.     

Molecular orbital calculations on complexes with strongly Jahn-Teller unstable transition metals: The hexanitro-copper(II) and cobalt(II) ions

INDO-LCAO-MO calculations have been performed for the complex cations [T^II(NO₂)₆]^4- (T^II: Cu²⁺, Co²⁺), in order to analyse the T-N bond properties and the Jahn-Teller distortion of the TN₆ octahedra as well as the high-spin low-spin behaviour of Co²⁺. While the essential features of the electronic structure and the coordination geometry of the TN₆ polyhedra resulting from the calculations are well in line with the experimental data for nitrocomplexes A₂^IM^IIT^II(NO₂)₆, the quantitative agreement is only approximate.     

Relaxation within the electronic ground state of the ferrous ion in [Fe(H2O)6]K2(SO4)2 single crystals at low temperatures

Single crystal Mössbauer spectra of [Fe(H₂O)₆]K₂(SO₄)₂ taken in external magnetic fields up to 5 T at low temperatures show large line broadenings, which are due to intermediate relaxation rates within the electronic orbital ground state. The spectra are fitted using a Blume stochastic relaxation model, the ferrous ion flipping between two electronic states. The results of the fit are discussed in a ligand field model of the hexaaquo-coordinated high-spin ferrous ion.     

Long-lived diatomic dications: potential curves and radiative lifetimes for CaBr2+ and CaI2+ including relativistic effects

Relativistic effective core potential calculations have been employed in the framework of a spin–orbit configuration interaction to compute the lowest-lying electronic states of the CaBr²⁺ and CaI²⁺ dications, and the results are compared with the data for the isovalent CaCl²⁺ system studied earlier. The ground X²Π state in all three dications arises from a strong polarization of X(²P°)(X= Cl, Br or I) by the Ca²⁺(¹S) ion and is bound by 0·96–1·55eV with respect to the corresponding diabatic dissociation limits. It is split by the spinorbit interaction into the X₁ ²Π_3/2 and X₂ ²Π_1/2 components, with the energy splittings calculated to be 647 cm^-1(CaCl²⁺), 2115 cm^-1(CaBr²⁺) and 3544 cm^-1(CaI²⁺). The X₁ and X₂ states are found to be thermodynamically stable in CaCl²⁺ and CaBr²⁺, while in CaI²⁺ the lowest dissociation limit, Ca⁺+(²S)+ I^{+ 3}P₂), lies 1700 and 5200 cm^-1 lower than the X₁ and X₂ minima respectively. The X₁ and X₂ states in CaI²⁺ are extremely long-lived, however, owing to the high and very broad potential barriers to dissociation. The first electronic excited state, A²σ⁺, is also bound in all the above systems, although it is pre-dissociated in CaBr²⁺and CaI²⁺ at large internuclear distances. All other low-lying electronic states of CaX²⁺ are repulsive. Electric-dipole moments are calculated for the A→ X₁, X₂ transitions. The corresponding radiative lifetimes are found to be very long in CaCl²⁺ : τ(A→X₁) = 19·3 ms and τ(A→X₂) = 9·9 ms (the values are given for ν' = 0), and become very significantly shorter for CaBr²⁺ and CaI²⁺ because of the stronger spin-orbit interaction in the heavier systems. This effect is especially noticeable for the A →X₂ transitions, for which the values are computed to be 364 μs in CaBr²⁺ and 50·3 μs in CaI²⁺. The theoretical data obtained should aid in the future spectroscopic detection of these species. To data no experiment of this type has been successfully carried out for any of the thermodynamically stable diatomic dications.     

First principles study on the electronic structure of the two chain compounds of [ M(N3)2(HCOO)][(CH3)2NH2] (M=Fe and Co)

First principles calculations have been performed to study the electronic structure and the ferromagnetic properties on the two chain compounds of [M(N₃)₂(HCOO)][(CH₃)₂NH₂] (M=Fe and Co). The relative stability of the ground state, the density of states and the electronic band structure are examined. The results reveal that antiferromagnetism (AFM) state is the ground state and ferromagnetism (FM) state is the metastable one for both of them. The two compounds exhibit semiconductor character with small gap in the FM state, while metallic in the AFM state. In the FM state, the magnetic moments mainly arise from the Fe and Co ions with little contribution from the nearest-neighboring N and O atoms due to the hybridization between the Fe or Co 3d states and the nearest-neighboring N and O 2p states.