The overlap matrix and the Slater-Koster interpolation scheme

The usual assumption of a unit overlap matrix in the LCAO interpolation scheme of Slater and Koster leads to an inconsistency, which is discussed in general terms and demonstrated for the layered 1T-polytype of the semiconductor ZrS₂.     

Density of states of the clean Mo (110) surface

The electronic structure of the (110) surface of Mo is calculated using transfer matrix method. The Hamiltonian is of tight-binding type with a basis of nine orbitals per atom. Spectral densities of states for special points of the 2-D Brillouin zone are presented on the surface and in the three consecutive layers. The band structure in the σ direction and the local density of states are also calculated. The results are compared with the few experimental data available in the literature.     

Low temperature 93Nb nuclear spin-lattice relaxation in Nb and NbMo alloys

High accuracy ⁹³Nb nuclear spin-lattice relaxation data are presented for Nb, Nb_0.75Mo_0.25, and Nb_0.70Mo_0.30 between 1.7 and 4.2 K. (T₁T)^?1 is independent of temperature and scales as the square of the density of states at the Fermi level.     

Structure of excited states in100Mo and102Mo from spectroscopy using18O induced reactions

The lifetimes have been determined for the 2⁺, 0^+～ and 4⁺ states in¹⁰⁰Mo and¹⁰²Mo using the recoil-distance Doppler-shift method. The states have been excited in¹⁰⁰Mo by Coulomb excitation and in¹⁰²Mo by the two-neutron transfer reaction induced by¹⁸O ions on a¹⁰⁰Mo target. The study of the excitation function for the elastic and inelastic scattering on the ground and first excited 2⁺ state in¹⁰⁰Mo at beam energies between 20 and 61 MeV shows that 40 MeV is the highest incident energy for pure Coulomb excitation. Above this energy nuclear absorption sets in and nuclear scattering contributes to the excitation of the 2⁺ state of¹⁰⁰Mo. From the lifetimes of the 2⁺ and 4⁺ states deformation parameters of ¦β¦= 0.21 and ¦β¦=0.31 for¹⁰⁰Mo and¹⁰²Mo respectively were deduced. The 0^+′ levels are not shape isomeric states, as suggested earlier, but they decay by enhancedE2 transitions to the first 2⁺ states. From a comparison with similar states in other transitional nuclei it is suggested that they are band heads forβ vibrational bands.     

Radiative lifetimes in Nb I and Mo I using a novel atomic beam source

A novel atomic beam source not used previously for lifetime measurements is described. It was employed in determining lifetimes of 6 levels of niobium which have not been measured previously. In addition liftimes of 6 molybdenum levels have been determined and are compared with data from the literature.     

Half-lives of levels in99Nb and99Mo

The half-lives of the 469-keV level in⁹⁹Nb and the 236-keV state in⁹⁹Mo have been determined to (0.21±0.06) ns and (0.87±0.15) ns, respectively, fromβ,γ-delayed coincidences. Values ofB(E2)=(89±28)e ² fm⁴ andB(M1)=(0.017±0.003) μ _n ² are deduced for the 469-keV transition in⁹⁹Nb and the 138-keV transition in99Mo. The result for theE2-transition probability seems to be in accordance with the particle-core coupling interpretation of the low-lying levels in⁹⁸Nb if⁹⁸Zr is used as the core. TheM1 probability for⁹⁹Mo agrees with the systematics for “l-forbidden” 1g_7/2→2d _5/2 neutron transitions.     

Slater-Koster parametrization of the band structure of TiNi

A very accurate Slater-Koster parametrization of the band structure of the intermetallic compound TiNi is presented. Various technical aspects of optimizing the Slater-Koster interpolation method for the CsCl structure are discussed.     

Atomic displacements in dilute alloys of Cr, Nb and Mo

Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and 4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe, Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10 NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also.     

Observation of superdeformed states in 88Mo

High-spin states in ⁸⁸Mo were studied using the Gammasphere germanium detector array in conjunction with the Microball CsI(Tl) charged-particle detector system. Three γ-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A= 80 region have been identified and assigned to the nucleus ⁸⁸Mo. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of β₂≈ 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three bands are assigned to two-quasi-particle proton configurations at superdeformed shape. Received: 20 May 1999 / Revised version: 25 August 1999     

Density of states of a disordered Hubbard model using the modified moments method

We apply the modified-moments method to compute the density of states of the impurity band of a doped semi-conductor in the intermediate region of impurity concentrations. This method is used to correct the density of states obtained by interpolating between the high and low concentration limit asymptotic expressions. The calculation is based on the Hubbard model in the atomic limit without spin ordering. The overlap integral is assumed to be a Gaussian function of the impurity separation. Use is made of the first seven moments of the exact distribution and of the low and high concentration limit approximations previously calculated. The first six moments are employed to determine the orthogonal polynomial expansion of the density of states while the seventh moment is used as a check on the accuracy of the distribution obtained. The results are similar to the previous ones using a truncated Edgeworth series for the correction term but the present method has the advantage of being a more systematic approach.     

New interpretation of surface states in W and Mo

The linear combination of muffin tin orbirtals (LCMTO) technique has been used to calculate surface states in the s, dz² band gap of W and Mo. These states are found to be very sensitive to surface reconstruction effects in that they become more localized and their energies shift by ～ 0.08 Ry. Furthermore, reconstruction reduces the dangling bond charge density in the vacuum region.     

Density of states of Zn and β-Brass

The X-ray photoemission spectrum of the valence band of β-Brass is compared with those of Cu and Zn and with a band structure calculation. The positions of thed-bands in the alloy are found to be readily explained by using the vacuum level as a reference.     

High-spin states in neutron-rich 102Mo nucleus

High-spin states in neutron-rich 102Mo nucleus have been studied by measuring the prompt γ-rays in the spontaneous fission of 252Cf. The previous level scheme has been updated and some new levels and transitions are identified. The one-phonon γ-band is expanded and a band head level of the two-phonon γ-band is proposed. The systematic characteristics of yrast bands, one-phonon γ-bands, two-phonon γ-bands and quasi-particle bands in 102Mo, 104Mo and 106Mo are discussed.     

γ-TiAl中Nb和Mo合金化效应的第一性原理研究

基于密度泛函理论框架下的第一性原理离散变分(DV)和DMol方法研究了4d过渡金属元素在γ-TiAl 中的择优占位行为及其Nb和Mo的合金化效应.转移能的计算结果表明Y，Zr，Nb，Mo在γ-TiAl中有Ti占位倾向，而Tc，Ru，Rh和Pb则表现为Al占位倾向.通过对差分电荷密度、Mulliken轨道集居数以及态密度的分析表明Nb和Mo可以提高杂质元素与其近邻基体元素之间的相互作用和相应原子之间的键合强度，导致较强的固溶强化效应. 关键词： 密度泛函理论 第一性原理 电子结构     

Odd neutron nuclei near A=100: Rotational bands in103Mo and105Mo populated in theβ − decays of103Nb and105Nb

Theβ ^? decays of¹⁰³Nb and¹⁰⁵Nb have been studied at the fission product separators JOSEF and LOHENGRIN. Half-lives of (1.5±0.2) s and (2.95±0.06) s, respectively, have been determined for these decays. Fromγ singles andγ-γ coincidence measurements extended level schemes for¹⁰³Mo and¹⁰⁵Mo have been established for the first time. The lowest energy levels of these nuclei are consistent with the interpretation as members of rotational bands built on a 3/2⁺ [411] Nilsson state. Evidence is presented for the location of the 9/2⁺ [404] configuration.     

Density of surface states of ordered adlayers

A method for calculating Green functions has been obtained by extending the continued fraction expansion method. It is applicable to a quasi-tridiagonal hamiltonian. The surface density of states of ordered adlayers has been studied by this method within the tight-binding approximation. Local densities of states of the outermost and the following few atomic planes are calculated for the (2 × 1) and (1 × 2) overlayer on a simple cubic (110) surface. It is found that the effect of long range order of the overlayer and of adsorption site is very important for the electronic structure of the adlayer. The nonbonding state, a new kind of surface state characteristic of the ordered adlayer, is obtained. It is shown that the energy of the nonbonding state degenerates at the orbital energy of an adatom when the direct interaction between adatoms is negligible, so that the states provide a strong peak in the adsorbate band for certain overlayer structures.