DV-Xα Molecular Orbital Calculation Research Articles

Ti–O coordination at a Pb(Zr,Ti)O3/Pt interface annealed in a hydrogen-containing ambient analyzed using spatially resolved electron energy-loss spectroscopy

We have investigated how annealing in a hydrogen-containing ambient changes the Ti–O coordination structure in a Pb(Zr,Ti)O3 (PZT) film fabricated on a Pt electrode by using spatially resolved electron energy-loss spectroscopy (EELS). Experimental results show that the Ti–O coordination structure was changed by the annealing at the PZT/Pt interface. However, there were no clear changes in the coordination number of O atoms to a Ti atom at the interface. Our EELS spectrum analysis using DV-Xα molecular orbital calculations indicates that the orbital overlaps between the 3d orbitals of a Ti atom and the 2p orbitals of the neighboring O atoms differ at the interface from those in the bulk PZT crystal. Therefore, our results indicate that the H2 annealing deformed the PZT crystal structure at the PZT/Pt interface, changing the Ti–O orbital overlaps. This structural change in the PZT film should be attributed to the marked decrease in Pb concentration at the H2-annealed PZT/Pt interface [N. Ikarashi, Appl. Phys. Lett. 73, 1955 (1998)].

Molecular orbital calculation of graphite K- V X-ray emission spectra

The DV-Xα molecular orbital (MO) calculation method has been applied to the carbon K- V X-ray emission spectra of graphite. The calculated 2 p density of states (DOS) of a larger model cluster, which avoided the influence of dangling bonds of the cluster edge, was in excellent agreement with the X-ray emission spectra. The calculated π and σ subbands of 2 p DOS explained the polarized behavior of the spectra. The orientation of graphite was quantitatively discussed by means of polarization of the spectra. These results were applied to the analysis of the structural change of mechanical milled graphite; the structure change of the ball-milled graphite was studied by the X-ray spectroscopy and MO calculation. It was shown that the refinement of graphite powder occurred for up to 1000 h of milling, keeping the graphite structure, and that a further milling changed the C-C bonding within the graphite layer network.

Correlation between the parameters obtained from the DV-Xα molecular orbital calculation and the partial molar enthalpies of formation for liquid Ni-, Fe-, Cr- and Ti-based transition metal alloys

The molecular orbital calculation has been conducted on Ni-, Fe-, Cr- and Ti-based transition metal alloys using the DV-Xα cluster method. The calculated parameters of the bond order and Md (average energy level of the d-orbital for alloying element) are compared with the experimental partial molar enthalpies of formation of liquid alloys and also with the Miedema's semi-empirical calculation. As a result, it is found that both the parameter Md and the calculated partial molar enthalpies of formation using the Miedema scheme correlate with the experimental partial molar enthalpies of formation. The partial molar enthalpies of formation become larger when there is a larger difference in the number of d-electrons between an alloying element and a base metal. As the ionicity of alloying elements correlates with the Md, charge transfer between an alloying element and a base metal is considered to contribute to the chemical bonding even in the transition-metal-based alloys.

Theoretical Study of Si <I>K</I><SUB>β</SUB> X-ray Fluorescence Spectrum of SiO<SUB>2</SUB>–Na<SUB>2</SUB>O Binary Slag by DV-Xα Molecular Orbital Calculation

A new method has been developed to simulate Si Kβ X-ray fluorescence spectra of SiO2–Na2O binary slags using the DV-Xα molecular orbital calculation. The composition of the slag has been incorporated for the first time in the calculation of the Si3p partial densitiy of states (PDOS). The calculated Si3p PDOS dealing with the Na2O content agreed well with the experimental Si Kβ X-ray fluorescence spectra of the 50 mol%SiO2-50 mol%Na2O and 33.3 mol%SiO2-66.7 mol%Na2O binary slags. The present method was found to provide a very useful means of clarifying the change in shape of the X-ray fluorescence spectrum of the slag with the metal oxide content, and also of understanding the concept of basicity at the same time.

Chemical change of nitrosylpentacyanoferrate(II) during XPS measurements: Identification of the irradiated product by DV-Xα molecular orbital calculations

A spectral change of the core and valence band levels for sodium nitrosylpentacyanoferrate(II) dihydrate, Na 2 [Fe(NO)(CN) 5 ]· 2H 2 O, has been observed during XPS measurements. The fresh sample had two peaks for N 1s at 402.9 and 398.8 eV, one peak for Fe 2p 3/2 at 710.6 eV and one peak for Fe 2p 1/2 at 723.5 eV. The irradiation of the sample by X-ray and e − flood decreased the intensity of the N 1s signal at 402.9 eV, and gave new peaks in 708.4 and 721.5 in the Fe 2p region. Irradiation also gave a peak of 1.5 eV in the valence band. The experimental results and a molecular orbital calculation by the DV-Xα SCF procedure suggest that the irradiated product of the compounds is [Fe(CN) 5 ] 3− or [Fe(CN) 5 (OH 2 )] 3− .

Estimation of the Dissolved Structures and Condensation Reactivities of Mononuclear Molybdenum(VI) Species in Solution Using the UV-vis Absorption Spectra and Molecular Orbital Calculation DV-Xα

Abstract The dissolved structures of the mononuclear molybdate species, MoO42−, HMoO4−, and H2MoO4, in aqueous solution were estimated by optimizing their structure models so that their UV-vis absorption spectra were well reproduced by the DV-Xα molecular orbital calculation. In this paper it is proposed that the former two species are tetrahedral ions, and the last is a distorted octahedral species. Using the values of the bond order obtained by a Mulliken population analysis the reason why the dimolybdate anion Mo2O72− does not exist, in contrast with the presence of the well-known dichromate anion Cr2O72−, has been explained. The key species which plays an important role in condensation reactions of molybdate system is not the HMoO4− ion, but the H2MoO4 with very weak Mo–OH bonds.

Simple correlation between Mn-K? X-ray emission and Mn 2p X-ray photoelectron spectra for high oxidation number or low-spin manganese compounds

The high-resolution Mn-Kα X-ray emission spectra (XES) and Mn 2p X-ray photoelectron spectra (XPS) for K[MnO4], K3[Mn(CN)5(NO)], K2[MnO4] and K3[Mn(CN)6] were measured. The first and second compounds which have no unpaired electrons, give symmetrical peaks in Mn-Kα1 XES and Mn 2p3/2 XPS spectra. The spectra of the other compounds show asymmetrical lines. When the lines are divided into two Lorenzian (for XES) or Gaussian (for XPS) curves, the energy separation and intensity ratio of the two peaks coincide with each other in both spectroscopies. These results are rationalized by spin-unrestricted DV-Xα molecular-orbital calculations of the anions. The electronic structures of these anions are calculated for their ground state and hole states in 1s and 2p levels. It is concluded that the electronic structures of the compounds in the ground states are conserved in the core hole states. Thus the satellite peaks due to charge transfer are not observed and the peak profiles are governed by the exchange splitting between 2p and valence electrons.

Correlation between Viscosity and Bond Order Calculated from the Molecular Orbital Theory for Molten SiO<SUB>2</SUB>

The correlation between viscosity of the molten SiO 2 and its bond order obtained by the DV-Xα molecular orbital calculation was examined. The bond order is a measure of strength of covalent bond. For the molten SiO 2 , the bond order between Si ion and O ion was very high. This high bond order value of the molten SiO 2 was considered to be the reason for the its high polymerization degree and the strong tendency of the localization of the Si ion near the O ion and resulted in the high viscosity

Structure and State-Energy Relationship of Photo-Excited Cu(I) Complex

Abstract Excited [CuI(dmphen)2]+ (dmphen = 2,9-dimethyl-1,10-phenanthroline) was studied in terms of its molecular structure. The MLCT (metal-to-ligand charge-transfer) transition energy and phosphorescence lifetime of the copper(I) complex in the solid state were reduced with diminishing the dihedral angle between two dmphen ligands. The results of a DV-Xα molecular orbital calculation were in good agreement with the spectroscopic results. In solution, the non-luminous character of [CuI(phen)2]+ (phen = 1,10-phenanthroline), which had no steric-hindered methyl groups retarding the flattening motion, was explained from lowering the lowest excited MLCT state due to a drastic distortion by the photoexcitation.

分子軌道法によるSiO<SUB>2</SUB>融体中のSiイオン周囲の局所的電子状態の検討

Local electronic states around Si ions in molten SiO2 have been investigated using DV-Xα molecular orbital calculation. Bond order and density of states were utilized to clarify the strength of the covalent bond between Si ion and O ion. It was found that the partial densities of states of 3s, 3p and 3d of the Si ions overlapped widely with the partial densities of states of 2p and 3s of the O ion. As a result, the bond order between the Si and O ions becomes very high, that is, the strength of the covalent bond becomes high. This is probably the reason for the formation of network structure in the molten SiO2. It is therefore considered that the molecular orbital calculation is useful in investigating the local electronic states of the molten SiO2.

特集 金属間化合物の粉末冶金と諸持性 反応焼結による新しいＡｌ‐Ｔｉ‐Ｎの系合金の作製（第３報） Ｌｉ２構造のＡｌ３Ｔｉ相の生成機構の検討

The mechanism of the crystal structure transformation of Al3Ti from DO22 to a high symmetry Ll2 by the addition of Cr, Mn or Ni was investigated using the DV-Xα molecular orbital calculation. The calculation suggested that Ti atoms were able to locate at the 2nd neighbor sites of Ti atoms by substituting of Cr. Mn or Ni atoms for a part of the Al atoms which were at the 1st neighbor sites of Ti atoms. This is the reason for the formation of the Al3Ti with the Ll2 crystal structure by the addition of Cr. Nn or Ni.

C K-V x-ray-emission spectra of solid C70 with comparison to C60.

Carbon K-V x-ray-emission spectra of solid C 70 and C 60 are measured, and the partial electron densities of states (DOS) are calculated by the discrete-variational (DV) Hartree-Fock-Slater (Xα) molecular-orbital (MO) method. The measured x-ray line shapes are compared with the calculated 2p DOS of C 70 and C 60 . The agreement between theory and experiment is satisfactory without any adjustable parameters in the DV-Xα MO calculations

DV-Xα Molecular Orbital Method for X-ray Absorption Near Edge Structure–Application to N2 and CrO42-

We have performed DV-Xα molecular orbital calculations for XANES of the N2 and CrO42- species to confirm our conclusions concerning the origin of shape resonances reported before. The theoretical spectra in the present work are in good agreement with the experimental spectra. Shape resonances for the N2 molecule are examined and, as well as the previous works, found to-be due to electron scattering by the attractive potential of molecule, neither due to centrifugal barrier nor another potential barrier.

NEW APPROACH TO ESTIMATE DISSOLVED STRUCTURE OF IONS IN SOLUTION

So far, if a species in solution exists in relation with some equilibria and its concentration is only a part of the total amount of the conjugating species, the estimation of the structure of the species in the solution has been very difficult. Recently, we developed a new approach which makes the estimation possible: The factor analysis with equilibrium constraints is applied to the UV/V spectra of the sample solutions with various pH values to extract the pure component spectrum of the target species; and thisspectrum is simulated by the DV-Xα molecular orbital calculation, changing the structure model of the species.

The lowest metal-to-bipyridine charge-transfer excited state of [Cr(2,2′-bipyridine)(CO)4

The DV-Xα molecular-orbital calculations have been carried out on [Crbpy(CO)4](bpy,2,2′-bipyridine) and its electron attachment and detachment products. The one-electron attachment of [Crbpy(CO)4] yields a complex of bipyridine anion radical, while the one-electron detachment results in ionization of the central metal atom. The lowest excited state of [Crbpy(CO)4] is the metal-to-ligand charge-transfer (MLCT) excited state which consists of the bipyridine anion radical and the central metal ionized. The transition-state calculation predicts the lowest MLCT excited states at around 23∼30×103 cm−1 and the lowest bipyridine (π,π*) excitations at 36×103 cm−1 and 42∼45×103 cm−1. The calculation also concludes that the MLCT excitation induces a counter migration of the other electrons not directly involved in the charge-transfer excitation. The configuration-interaction calculations predict the lowest MLCT excited singlet states at around 21∼35×103 cm−1 and the lowest bipyridine (π, π*) excited singlet states a...

A relativistic muffin-tin free Xα molecular orbital study of metal tetrakis tetrahydroborates: M(BH 4) 4, M = Zr, U

Muffin-tin free DV-Xα molecular orbital calculations employing self-consistent numerical basis sets have been performed for the tetrakis tetrahydroborates of zirconium and uranium. For the latter compound, both a nonrelativistic and a fully relativistic solution have been obtained. These calculations essentially confirm the results of a recent extensive Xα-SW study on the electronic structure of tetrahydroborates. Very good agreement with experimental ionization potentials is found in the present calculation. The assignment of the most important ligand metal bonding orbitals to the first PE band of Zr(BH 4) 4 supports that of the Xα-SW study, but is at variance with the results of a previous STO-DV-Xα investigation. A relativistic treatment is mandatory for a proper description of the metal ligand bonding in the uranium complex. In the nonrelativistic calculation the contribution of U 5f orbitals to metal ligand covalency is overestimated, the participation of the U 6d orbitals in such bonding is underestimated. These findings parallel the results of a previous Xα-SW study on uranocene, U(C 8H 8) 2, where this effect has been rationalized as a pecularity of the Xα method.

The 5d← 4fexcited states of [Ce(OH2)9]3+

A DV-Xα molecular-orbital calculation was carried out on [Ce(OH2)9]3+. The charge donation of coordinated water molecules results in a net charge of +0·354 on the central tervalent metal ion and an appreciable polarization in the coordinated waters. The coordination bond of the vertex waters is stronger than that of the equatorials. The observed transition moments and energies of the 5d ← 4f excitations as well as the observed ligand-field splitting of 2 D(5d 1) multiplet in the D 3h ligand field of [Ce(OH2)9]3+ were reasonably reproduced by use of the transition-state approximation on the base of DV-Xα molecular-orbital calculation. The model also predicts a contraction of 4f orbital while an expansion of 5d orbital in the cluster. The one-electron energies of 4f, 5d and 6s orbitals as well as the spin-orbit coupling energies in Ce3+ free ion were also calculated by the relativistic DV-Xα method. The relativistic equation reproduces the observed values only for α = 1·0 rather than the traditional value α = 0·7.