DV-Xa molecular orbital calculation

Novel Theoretical Prediction Method of the Haldane Gap among the Azido-Bridged Compounds by DV-Xa Molecular Orbital Calculation Tomohiko Ishii, Yukikazu Fuke, Naoko Aizawa and Masahiro Yamashita ... 

The DV-Xa molecular orbital calculational method used here utilizes basis sets of numerically calculated atomic orbitals, as well as those of analytical atomic orbitals such as Slater orbitals. Matrix element of the Hamiltonian and the overlap integral are calculated numerically by summing integrand at sampling points rk, the Diophantine points, which are distributed according to the weighted function, and expressed as. 

Theoretical studies on the atomic number dependence of the relative effects on chemical bonding, including polonium, have been carried out, " for example PoFg was investigated. An analysis of bond overlap population using both nonrelativistic and relativistic DV-Xa molecular orbital calculations was... 

To clarify the origin of thermal stability of transition metal nitrides, an empirical approach and the DV-Xa molecular orbital calculation for several transition metal nitride have been executed. Thermally stable crystal phases in MOj jM N (M =Nb, Zr,... 

It has been found for examining empirically the thermal properties of the metal nitrides that the number of valence electrons is more advantageous than the average number of valence electrons per atom. DV-Xa molecular orbital calculations for several metal nitrides reveal that the thermal stability of transition metal nitride is intensely dominated by the bond overlap population of the metal-metal bond. 

DV-Xa molecular orbital calculation is demonstrated to be very efficient for theoretical analysis of the photoelectron and x-ray spectroscopies. For photoelectron spectroscopy, Slater s transition state calculation is very effective to give an accurate peak energy, taking account of the orbital relaxation effect. The more careful analysis including the spin-polarized and the relativistic effects substantially improves the theoretical results for the core level spectrum. By consideration of the photoionization cross section, better theoretical spectrum can be obtained for the valence band structure than the ordinary DOS spectrum. The realistic model cluster reproduce very well the valence state spectrum in details. 

In the present work, the structure of the [Ni (CgO)4dpg 2] complex at various temperatures, from room temperature (r.t.) to 220°C, is investigated by Ni-A XANES spectra measurements and by DV-Xa molecular orbital calculations. 

In the present study, we synthesized dibromo(l,4,8,ll-tetraazacyclotetradecane)copper(II) ([CuBr2(cyclam)]) and diaqua(l,4,8,ll-tetraazacyclotetradecane)copper(II) difluoride four hydrate ([Cu(cyclam)-(H20)2]F2 4H20) complexes and performed single crystal structure analysis and X-ray absorption near-edge structure (XANES) measurements in crystals and in aqueous solution. Furthermore, DV-Xa molecular orbital calculations have been made for models based on these results, and the structures and electronic states of the [Cu(cyclam)] complexes in crystals and in aqueous solution are discussed, in particular, on the axial coordination to Cu(II). 

A Method of Incorporating the Composition into the Calculation of the O K X-ray Emission Spectrum of the Glassy State SiOj—Na O Binary Slag with the DV-Xa Molecular Orbital Calculation... 

We calculated the DOSs of Mg, Ti, Co, Cu and Zn with stacking faults using the DV-Xa molecular orbital calculation method. For all these metals the DOSs for the equilibrium h.c.p. structures were at lower energy than the corresponding f.c.c. structures. This suggests that the work function of Cu alone is expected to be lowered by formation of the stacking faults but those of the other metals remain unchanged. 

In the present study, the y values of the compounds were determined by measuring the Cp values at very low temperatures. Also, the y values obtained were compared with the DOS calculated by the DV-Xa molecular orbital method [4], In addition, the Debye temperature, the standard entropy of formation, the electric resistivity p and the thermal conductivity k were further determined for each compounds. The physico-chemical properties of the compounds were discussed from both views of the electronic and lattice vibration states. 

To obtain a qualitative picture of the complex structure of SO3 adsorbed on the Pt (111) surface, the density of states (DOS) was calculated from the DV-Xa molecular orbital method. The level width was broadened by a Gaussian function (1.0 eV FWHM) to mimic the solid state. The results of the studies are summarized in the following paragraphs. In each DOS, Fermi energy is set at 0. In configuration A, the adsorbed O atoms are classified as of two types. One is two O atoms bound to Pt surface atom (0(1)) and the other is one O atom unbound to Pt surface (0(2)). 

We evaluated adsorbed SO3 configuration on Pt (111) surface by using the first-principles calculations with a slab model in a periodic boundary condition. On the basis of the result of the calculations with a slab model, we evaluated the electronic states of SO3 in detail using the relativistic DV-Xa molecular orbital method. 

In the present calculation, we used two ab initio methods to investigate structural stability and the potential for carrier generation of X B6 and X Bi2 clusters in c-Si. Here X is from H to Br in the periodic table. The following two methodsused were (i) plane wave ultrasoft pseudopotential method for the optimization of atomic structures and (ii) discrete variational-Xa (DV-Xa) molecular orbital method for the analysis of the fine electronic structures and activation energies of the clusters. 

The electronic structures of a series of models were calculated using the first-principles discrete variational-Xa (DV-Xa) molecular orbital (MO) method with a... 

The DV-Xa molecular orbital (MO) calculations were performed to analyze the Li-K XANES spectra of lithium halides powder. The computational details of the DV-Xa method have been previously described [10]. In this method, the exchange-correlation interaction, Vxcr between electrons is given by the Slater s Xa potential,... 

The electronic state calculations of transition metal clusters have been carried out to study the basic electronic properties of these elements by the use of DV-Xa molecular orbital method. It is found that the covalent bonding between neighboring atoms, namely the short range chemical interaction is very important to determine the valence band structure of transition element. The spin polarization in the transition metal cluster has been investigated and the mechanism of the magnetic interaction between the atomic spins has been interpreted by means of the spin polarized molecular orbital description. For heavy elements like 5d transition metals, the relativistic effects are found to be very important even in the valence electronic state. 

Theoretical photoelectron spectrum has been calculated by the use of DV-Xa molecular orbital method combined with the calculation of atomic photoionization cross section in Hartree-Fock-Slater model. A calculation of the photoionization cross section has been performed for flexible numerical atomic orbitals including the excited atomic orbitals which are employed for basis functions in the molecular orbital calculation. Some variation of the photoionization cross section is seen when a reconstruction of the atomic orbital due to change in the effective charge takes place. This affects the molecular photoelectron spectrum to a certain extent. 

The electronic structure of microcrystalline silicon of one-dimensional (1-D), 2-D, and 3-D clusters were calculated using the Discrete-Variational (DV)-Xa Molecular-Orbital method. The calculated results are discussed with respect to the effect of the size and the number of dimensions on the energy levels of molecular orbitals. The energy-gap (Eg) between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) decreases with the increase of cluster size amd the number of dimensions. It is found that including silicon 3d orbitals as basis sets decreases the Eg value. The results show that the components of silicon 3d orbitals in the unoccupied levels near LUMO are over 50 per cent. The calculated results predict that the Eg value will be close to the band gap of crystalline silicon when a 3-D cluster contadns more than 1000 silicon atoms with a diameter of 4nm. 

With the use of the DV-Xa molecular orbital method, electronic structure calculations have been performed to investigate the impurity effect on material properties. Firstly, calculations were done for F atoms substituted for 0 (oxygen) atoms in copper oxide superconductors. It was found that the population of the atomic orbitals of F atoms is small in HOMO (highest occupied molecular orbital) and a small fraction of charge carriers enters the impurity sites. The F impurities are therefore expected to be effective for pinning magnetic flux lines in Cu oxide superconductors. 

The electronic state calculation by discrete variational (DV) Xa molecular orbital method is introduced to demonstrate the usefulness for theoretical analysis of electron and x-ray spectroscopies, as well as electron energy loss spectroscopy. For the evaluation of peak energy. Slater s transition state calculation is very efficient to include the orbital relaxation effect. The effects of spin polarization and of relativity are argued and are shown to be important in some cases. For the estimation of peak intensity, the first-principles calculation of dipole transition probability can easily be performed by the use of DV numerical integration scheme, to provide very good correspondence with experiment. The total density of states (DOS) or partial DOS is also useful for a rough estimation of the peak intensity. In addition, it is necessary lo use the realistic model cluster for the quantitative analysis. The... 

In order to make a correct analysis of such an experimental spectrum, an appropriate theoretical calculation is indispensable. For this purpose, some of calculational methods based on the molecular orbital theory and band structure theory have been applied. Usually, the calculation is performed for the ground electronic state. However, such calculation sometimes leads to an incorrect result, because the spectrum corresponds to a transition process among the electronic states, and inevitably involves the effects due to the electronic excitation and creation of electronic hole at the core or/and valence levels. Discrete variational(DV) Xa molecular orbital (MO) method which utilizes flexible numerical atomic orbitals for the basis functions has several advantages to simulate the electronic transition processes. In the present paper, some details of the computational procedure of the self-consistent-field (SCF) DV-Xa method is firstly described. Applications of the DV-Xa method to the theoretical analysises of XPS, XES, XANES and ELNES spectra are... 

MOs) and MO energies of the impurity states are calculated by the DV-Xa molecular orbital method (18) in the second step, the many-electron Hamiltonian, in which the interactions between two electrons are exactly described, is diagonalized within a subspace spanned by Slater determinants made up of the obtained one-electron MOs. 

In the first step, the DV-Xa molecular orbital method is carried out self-consistently, in which the exchange and correlation energies are taken into account by the use of Xa potential given by Slater (19). In the present calculations, the coefficient a is fixed at 0.7, which was found to be an appropriate value (20). The MOs are expressed as linear combinations of atomic orbitals (LCAOs). These atomic orbitals are numerically adjustable to the chemical environment in each iteration. The details of the DV-Xa method have been described by Adachi et al. (18). 

The first-principles calculations for theoretical XANES spectra consist of three procedures, that is obtaining the self-consistent charge density, the discretized continua and the X-ray absorption spectra. The self-consistent charge densities for the chemical species were calculated with software called SCAT which implemented the DV-Xa molecular orbital method (15). For calculations of the continua and X-ray absorption spectra, the method was extended within the framework of square-integrable (L ) discretized wavefunction method (9-11). 

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