Nd高掺杂锐钛矿相TiO2电子结构和吸收光谱的第一原理研究

基于密度泛函理论平面波超软赝势方法, 采用第一原理研究未掺杂和不同浓度Nd高掺杂锐钛矿相TiO₂的电子结构和吸收光谱. 计算结果表明, 在本文限定的Nd高掺杂浓度范围内, Nd高掺杂浓度越小, 锐钛矿相TiO₂的禁带宽度越窄, 吸收光谱发生红移越显著. 计算结果与实验结果变化趋势相一致.     

Model calculation of the electronic structure and spectroscopy of Hg2

Energy curves and transition moments of the excited valence states of Hg₂ were obtained in a model calculation based on calculated Mg₂ energy levels and the assumption that the asymptotic spin-orbit matrix elements for the Hg atom are applicable to the molecular states. The spin-orbit and orbital-rotational interaction of the excited states of Hg₂ is analyzed in both a Hund's case (c) and (a) representation. The intermediate (a) → (c) transition moments are obtained as a function of the internuclear distance. The effect of the orbital-rotational interaction which introduces Hund's case (b) and (e) couplings is found to be small for transitions among excited states under the conditions normally encountered for populating excimer states.Using the energy level positions and transition moments, the observed spectra and predicted spectra are compared for both radiative transitions including the ground state and among the excited states. The lifetime of the $\text{1}{}_{\mathrm{u}}\text{(}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{)}$ excimer state is calculated to be 1.4 μsec with the 335 nm band assigned to the $\text{1}{}_{\mathrm{u}}\text{→ X}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transition. The 485 nm bands cannot be assigned to any Hg₂ transitions. Strong bound-continuum absorptions are predicted for the 485 nm bands. On the other hand, the 335 nm emission is predicted to be absorbed by bound-bound transitions only.     

Cluster calculation of electronic structure and hyperfine interactions for α-Fe2O3

The MSX_α cluster technique has been used to study the electronic structure of hematite α-Fe₂O₃, where iron is formally in a 3d₅⁶S state. The calculated energy levels are compared with X-ray emission and photoelectron spectra. The wave functions have been used to compute the charge distribution, as well as hyperfine parameters such as quadrupole coupling constant, isomer shift and magnetic hyperfine field. The results indicate a considerable influence of chemical bonding on these parameters due to charge transfer and covalency. From the calculated field gradient and the measured quadrupole coupling constant a nuclear quadrupole moment for ^57mTe of about 0.11b is deduced. This value is smaller than the most recent estimates of 0.15b based on the ionic model but not as small as the value of 0.082b obtained from first principles calculations on iron dihalides.     

Upconversion from the I13/2 and I11/2 levels in Er:YAG

The efficiency of erbium three-micron laser (laser transition ⁴I_11/2→⁴I_13/2) depends essentially on the ratio of the parameters of active energy transfer upconversion (ETU) from the laser levels. The parameters of both ETU processes can be obtained from the analysis of the shape of the kinetics of the ⁴I_11/2 level in concentrated Er:YAG crystals, under short pulse pumping. Mathematical modeling is used to evaluate the sensitivity of the method and to estimate the errors which can be introduced by the inhomogeneous pumping and accidental impurities. It was found that the ratio of the parameters corresponding to the ETU from the laser levels is less sensitive to the pumping inhomogeneities than that corresponding to the lower laser level. A reduction of this ratio with increasing erbium concentration is observed.     

Experimental and theoretical investigations into the electronic structure of CF2Br2 by electron momentum spectroscopy

The binding energy spectra and electron momentum density distributions for the valence orbitals of CF₂Br₂ have been obtained by using electron momentum spectroscopy (EMS) at an impact energy of 1200 eV plus binding energy. The measured electron momentum profiles are compared with Hartree–Fock (HF) and density functional theory (DFT) calculations with different-sized basis sets. In general, the DFT-B3LYP calculation using the large basis sets of 6-311++G** and aug-cc-pVTZ fairly describe the experimental results. Moreover, the controversial orderings of the outer valence orbitals have been reassigned. The pole strength of the main ionization transition from the inner valence orbital of 1b₂ is determined.     

Electronic structure of CeAl2 thin films studied by X-ray absorption spectroscopy

We report X-ray absorption near edge structures (XANES) study of CeAl₂ thin films of various thicknesses, 40-120 nm, at Al K- and Ce L₃-edges. The threshold of the absorption features at the Al K-edge shifts to the higher photon energy side as film thickness decreases, implying a decreased in Al p-orbital charges. On the other hand, from Ce L₃-edge spectra, we observed a decrease in the 5d4f occupancy as the surface-to-bulk ratio increases. The valence of Ce in these thin films, as revealed by the Ce L₃-edge spectral results, is mainly trivalent. From a more detailed analysis we found a small amount of Ce⁴⁺ contribution, which increases with decreasing film thickness. Our results indicate that the surface-to-bulk ratio is the key factor which affects the electronic structure of CeAl₂ thin films. The above observations also suggest that charge transfer from Al to Ce is associated with the decrease of the film thickness.     

The electronic structure of CeO2 and PrO2

We have determined the electronic structure of CeO₂ and PrO₂ by performing SCF band calculations. We find that in both systems there are metal f- and d- electrons in the oxygen 2p bands. We discuss the question of valency and ionicity in these systems.     

The magnetic hyperfine structure in the rotational spectrum of H2CNH

The hyperfine structure in the ground-state rotational spectrum of methanimine was studied in the frequency range of 64-172 GHz by means of the Lamb-dip technique. This allowed to resolve, in some hyperfine components due to the ¹⁴N nucleus, doublets separated by only some tenth of kHz. We explain the splittings as due to magnetic interactions of the three protons with their molecular environment. The analysis of the experimental spectrum has been guided by quantum-chemical calculations of the hyperfine parameters.     

Concentration-dependent electronic structure and optical absorption properties of B-doped anatase TiO2

The concentration-dependent electronic structures and optical properties of B-doped anatase TiO₂ have been calculated using the density functional theory. The calculated results indicate that the electronic structures of B-doped TiO₂ have changed compared with those of pure TiO₂, which is mainly due to the new midgap states induced by B doping. As to the optical properties, we calculate the imaginary part of dielectric function ε₂(ω) and optical absorption spectra of pure and B-doped TiO₂. Two transitions E₁ and E₂ emerged after B doping. The intensity of absorption is enhanced by B doping both in the UV and visible regions. According to the results of imaginary part of dielectric function ε₂(ω) and DOS, it can be concluded that the two optical transitions correspond to the transitions from the O 2p states in the top of valence band to the midgap states and from the midgap states to the Ti 3d states in the bottom of conduction band, respectively. These results have important implications for the further development of photocatalytic materials.     

Crystal structure, electronic and transport properties of AgSbSe2 and AgSbTe2

Undoped and p- and n-doped AgSbX₂ (X=Se and Te) materials were synthesized by direct fusion technique. The structural properties were investigated by X-ray diffraction and SEM microscopy. The electrical conductivity, thermal conductivity and Seebeck coefficient have been measured as a function of temperature in the range from 300 to 600 K.To enlighten electron transport behaviours observed in AgSbSe₂ and AgSbTe₂ compounds, electronic structure calculations have been performed by the Korringa-Kohn-Rostoker method as well as KKR with coherent potential approximation (KKR-CPA) for ordered (hypothetical AgX and SbX as well as AgSbX₂ approximates) and disordered systems (Ag_1−xSb_xX), respectively. The calculated density of states in the considered structural cases shows apparent tendencies to opening the energy gap near the Fermi level for the stoichiometric AgSbX₂ compositions, but a small overlap between valence and conduction bands is still present. Such electronic structure behaviour well agrees with the semimetallic properties of the analyzed samples.     

Reanalysis of the D → X fluorescence spectrum of I2

The uv fluorescence spectrum of I₂ excited by iodine atomic radiation at 1830 Å is photographed and analyzed using a direct least-squares-fitting method with consistency constraints on the centrifugal distortion constants. The analysis confirms Verma's [J. Chem. Phys.32, 738–749 (1960)] prior analysis of this spectrum and yields improved molecular constants for v = 0–99 of the X state and $\text{v ? 204–208}$ of the D state.     

The absorption spectrum of the Ag2 molecule

The high dispersion absorption spectrum of the Ag₂ molecule has been photographed in the ～5300–1500-Å region. Observations include the previously reported A ← X, B ← X, C ← X, D ← X, and E ← X transitions and a new H ← X transition which occurs in the vacuum ultraviolet. Extensive spectral blending precluded detailed rotational analyses, but the band structures are consistent with $\text{ΔΩ}\text{= 0}$ and $\text{ΔΩ}\text{≥1}$ for D-X and C-X, respectively. The H state is perturbed and probably predissociated. The following molecular constants (in cm^?1) were obtained from fitting bandhead data to the usual expressions:

     

13.

Chemiluminescence of IF in the gas phase reaction of I₂ with F₂     

John W. Birks  Steven D. Gabelnick  Harold S. Johnston 《Journal of Molecular Spectroscopy》1975,57(1):23-46

Emission from both the state and the previously unreported $\text{A}{}^3\text{Π}{}_1$ state of IF has been observed in the gas phase reaction of I₂ with F₂ at low pressures. For the state the transition moment and vibrational populations were extracted from the spectra by a least-squares method whereby theoretical band shapes were fit to the experimental data. The effect of flow rates of reactants and Ar on the relative emission from the two electronic states, the effect of pressure on the state, and extinction of emission near 470 nm all favor the population of excited electronic states through a four-center reaction complex, rather than association of F and I atoms.It is argued that there is an avoided curve crossing between the lowest two ³Π_0⁺ states of IF, and that the ground state dissociation energy is 23 229 ± 100 cm^?1. The radiative lifetime of the state is estimated to be 10^?3 sec and to be much shorter than that of the $\text{A}{}^3\text{Π}{}_1$ state.     

14.

The electronic structure and properties of the C15 compounds CeAl₂, LaAl₂ and YAl₂     

T. Jarlborg  A.J. Freeman  D.D. Koelling 《Journal of magnetism and magnetic materials》1986,60(2-3):291-305

Results of self-consistent band calculations are reported for the C15 structured XAl₂ materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl₂) or at (CeAl₂) the Fermi energy. In paramagnetic CeAl₂, the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl₂. The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ_B per Ce atom in very good agreement with the maximum moment, 0.89μ_B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl₂ (i.e., no 4f electron) rather than that of CeAl₂.     

15.

Study of the electronic structure and spectral features of TiS₂,ZrS₂ and HfS₂ by the X_α discrete variational method     

S.P. Friedman  V.P. Zhukov  V.A. Gubanov 《Solid State Communications》1980,36(6):559-562

In order to study the electronic structure of TiS₂, ZrS₂ and HfS₂, selfconsistent charge X_α discrete variational calculations of clusters MeS₆^8- (Me = Ti, Zr, Hf) have been performed. The results obtained are consistent with band structure calculations. The covalency of the chemical bonding is shown to increase in the series TiS₂-ZrS₂-HfS₂, which corresponds to the atomization energy in the series. The results are applied in the interpretation of X-ray emission, photoelectron and optical spectra.     

16.

Tin hyperfine fields in Co₂ VSn and Co₂ NbSn from Mössbauer spectroscopy     

I. Vincze  W. Koch  E. Baggio-Saitovitch  Keizo Endo 《Solid State Communications》1976,19(10):997-999

The hyperfine fields at the Sn sites in the Heusler type alloys Co₂ VSn and Co₂NbSn have been measured by the Mössbauer effect at 4.2 K to be + 9.9 and + 15.0 kOe, respectively. These anomalously small values are discussed in terms of the outer electron structure of these alloys.     

17.

Photoelectron and electronic absorption spectra of SCl₂, S₂Cl₂, S₂Br₂ and (CH₃)₂S₂     

Richard J. Colton  J.Wayne Rabalais 《Journal of Electron Spectroscopy and Related Phenomena》1974,3(5):345-357

Photoelectron and electronic absorption spectra of SCl₂, S₂Cl₂, S₂Br₂, and (CH₃)₂S₂ have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MO's are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential.     

18.

Elastic and electronic properties of BeB₂ in comparison to superconducting MgB₂ and NbB₂     

A.K.M.A. Islam  F.N. Islam  Abraham F. Jalbout  Ludwik Adamowicz 《Solid State Communications》2006,139(6):315-320

A study of the structural, elastic and electronic properties of BeB₂, a promising diboride in view of the lighter mass of Be, has been made using self-consistent Density Functional Theory (DFT). The five independent elastic constants of BeB₂ are predicted for the first time. The elastic behaviour of the compound is compared with those of the superconducting MgB₂ and NbB₂. We also evaluate the electronic structure of BeB₂ in order to obtain further insight into its surprising difference from the superconducting MgB₂.     

19.

Three-dimensional electronic structure in highly doped Na_xCoO₂ studied by angle-resolved photoemission spectroscopy     

Toshiyuki Arakane  Takafumi Sato  Takenori Fujii 《Journal of Physics and Chemistry of Solids》2011,72(5):552-555

We have investigated three-dimensional electronic structure for Na_xCoO₂ (x=0.77 and 0.65) by high-resolution angle-resolved photoemission spectroscopy to study the origin of antiferromagnetic (AF) transition of highly doped Na_xCoO₂(x>0.75). The a_1g large hole-like Fermi surface (FS) in x=0.77 shows distinct three-dimensionality along the k_z direction, and a three-dimensional small electron pocket appears around Γ point, indicating strong inter-layer electronic correlation. On the other hand, x=0.65 sample does not show three-dimensional behavior. This result indicates that transition of FS as a function of band filling is closely related to the occurrence of the magnetic transition in highly doped Na_xCoO₂.     

20.

The C₂H₂ absorption spectrum in the Nd laser range     

L.N. Sinitsa 《Journal of Molecular Spectroscopy》1980,84(1):57-59

     

State	Te	ωc	Xωt
X	0.0	192.0	0.58
B	35 838.6	151.8	0.87
C	37 631.6	171.0	0.84
D	39 014.5	168.2	1.20
E	40 159.9	146.1	1.58
H	58 273.1	165.9	2.46

Chemiluminescence of IF in the gas phase reaction of I2 with F2

Emission from both the state and the previously unreported $\text{A}{}^3\text{Π}{}_1$ state of IF has been observed in the gas phase reaction of I₂ with F₂ at low pressures. For the state the transition moment and vibrational populations were extracted from the spectra by a least-squares method whereby theoretical band shapes were fit to the experimental data. The effect of flow rates of reactants and Ar on the relative emission from the two electronic states, the effect of pressure on the state, and extinction of emission near 470 nm all favor the population of excited electronic states through a four-center reaction complex, rather than association of F and I atoms.It is argued that there is an avoided curve crossing between the lowest two ³Π_0⁺ states of IF, and that the ground state dissociation energy is 23 229 ± 100 cm^?1. The radiative lifetime of the state is estimated to be 10^?3 sec and to be much shorter than that of the $\text{A}{}^3\text{Π}{}_1$ state.     

The electronic structure and properties of the C15 compounds CeAl2, LaAl2 and YAl2

Results of self-consistent band calculations are reported for the C15 structured XAl₂ materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl₂) or at (CeAl₂) the Fermi energy. In paramagnetic CeAl₂, the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl₂. The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ_B per Ce atom in very good agreement with the maximum moment, 0.89μ_B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl₂ (i.e., no 4f electron) rather than that of CeAl₂.     

Study of the electronic structure and spectral features of TiS2,ZrS2 and HfS2 by the Xα discrete variational method

In order to study the electronic structure of TiS₂, ZrS₂ and HfS₂, selfconsistent charge X_α discrete variational calculations of clusters MeS₆^8- (Me = Ti, Zr, Hf) have been performed. The results obtained are consistent with band structure calculations. The covalency of the chemical bonding is shown to increase in the series TiS₂-ZrS₂-HfS₂, which corresponds to the atomization energy in the series. The results are applied in the interpretation of X-ray emission, photoelectron and optical spectra.     

Tin hyperfine fields in Co2 VSn and Co2 NbSn from Mössbauer spectroscopy

The hyperfine fields at the Sn sites in the Heusler type alloys Co₂ VSn and Co₂NbSn have been measured by the Mössbauer effect at 4.2 K to be + 9.9 and + 15.0 kOe, respectively. These anomalously small values are discussed in terms of the outer electron structure of these alloys.     

Photoelectron and electronic absorption spectra of SCl2, S2Cl2, S2Br2 and (CH3)2S2

Photoelectron and electronic absorption spectra of SCl₂, S₂Cl₂, S₂Br₂, and (CH₃)₂S₂ have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MO's are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential.     

Elastic and electronic properties of BeB2 in comparison to superconducting MgB2 and NbB2

A study of the structural, elastic and electronic properties of BeB₂, a promising diboride in view of the lighter mass of Be, has been made using self-consistent Density Functional Theory (DFT). The five independent elastic constants of BeB₂ are predicted for the first time. The elastic behaviour of the compound is compared with those of the superconducting MgB₂ and NbB₂. We also evaluate the electronic structure of BeB₂ in order to obtain further insight into its surprising difference from the superconducting MgB₂.     

Three-dimensional electronic structure in highly doped NaxCoO2 studied by angle-resolved photoemission spectroscopy

We have investigated three-dimensional electronic structure for Na_xCoO₂ (x=0.77 and 0.65) by high-resolution angle-resolved photoemission spectroscopy to study the origin of antiferromagnetic (AF) transition of highly doped Na_xCoO₂(x>0.75). The a_1g large hole-like Fermi surface (FS) in x=0.77 shows distinct three-dimensionality along the k_z direction, and a three-dimensional small electron pocket appears around Γ point, indicating strong inter-layer electronic correlation. On the other hand, x=0.65 sample does not show three-dimensional behavior. This result indicates that transition of FS as a function of band filling is closely related to the occurrence of the magnetic transition in highly doped Na_xCoO₂.