Jai Sam Kim

The adsorption of hydrogen on B2 TiFe surfaces

We investigate the interaction of hydrogen with the B2 TiFe (001) and (110) surfaces using the full-potential linearized augmented plane wave (FLAPW) method. The changes in the electronic structures in the di6erent B2 TiFe surfaces in comparison with the bulk ground state are analyzed. Ferromagnetic order is found in the Fe-terminated (001) surface with the magnetic moment 2:27� B, which quickly diminishes inside the 8lm. The absorption of hydrogen onto the Fe=TiFe (001) surface results in a decrease in the magnetic moment. For the fully relaxed surfaces interacting with hydrogen, the driving bonding mechanisms for di6erent adsorption sites are discussed. A microscopic explanation of the local surface reactivity is given. It is found that the hydrogen atoms form stronger chemical bonds with the iron atoms than with the titanium atoms in the B2 TiFe surfaces. ? 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

The electronic properties of FeCo, Ni3Mn and Ni3Fe at the order–disorder transition

Electronic structure calculations of the ordered ferromagnetic and paramagnetic transition metal alloys FeCo, Ni3Fe andNi 3Mn are performedusing the full-potential linearizedaugmentedplane wave method . The evolution of the electronic structure of alloys at disordering is studied in the framework of the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) combined with the local-density functional method. It is shown that the value of the magnetic moment is insensitive to order in all of the alloys investigated. The changes in the optical conductivity spectrum at the order–disorder transition are discussed. r 2002 Elsevier Science B.V. All rights reserved.

SU(N) Higgs problem with adjoint representation, and Michel's conjecture

Abstract Recently a geometrical method has been devised for analyzing the minimum of complicated Higgs potentials. Using the method we analyze the general quartic Higgs potential, including cubic coupling, for SU( N ) adjoint representation. The task of proving Michels conjecture is reduced to showing that the orbit space is generally “star-shaped”.

Electronic structure of binary and ternary Ti-based shape-memory alloys

Abstract The electronic and structural properties for TiMe (Me=Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) alloys are studied using the full-potential linearized augmented plane wave (FLAPW) method. The alteration of electronic structure with disorder and alloying with a third element is analyzed. The calculated emission, absorption X-ray and electron energy-loss spectra are found to be in good agreement with experiments.

Hydrogen adsorption on Pd/TiFe (110) surface

Adsorption of hydrogen on the TiFe (110) surface covered by palladium monolayer was investigated using the full potential linearized augmented plane wave method within the local density approximation. Influence of palladium coating to adsorption properties of the TiFe (110) surface as well as difference it from Pd/TiFe (100) are discussed.

SU(5) Higgs problem with adjoint + vector representations☆

Recently Kim has given a general method, using group-invariant orbit parameters, for determining the energy and residual symmetry of the Higgs potential minimum. In this paper we illustrate the method by working out the case of a quartic SU(5) Higgs potential with 5 and 24 higgsons. In this method the Gell-Mann-Slansky conjecture concerning possible little groups of the potential minimum takes a geometric form, which is verified for our case. The results are used to discuss the hierarchical symmetry breaking of SU(5) grand unification theory. We generalize our results to the SU(N) adjoint + vector models, which are all closely related.

Theoretical study of the electronic structure and hydrogen adsorption properties in B2-TiFe thin films with Pd coating

Abstract The electronic structure of Pd-covered TiFe (0 0 1) surface was studied using the full-potential linearized augmented plane wave method with local density approximation for the exchange-correlation potential. The electronic structure changes introduced by Pd in the surface layers of B 2 -TiFe (0 0 1) are analyzed. The influence of hydrogen and oxygen on the electronic properties and surface electronic structure of clean B 2 -TiFe (0 0 1) and with monolayer of Pd is discussed.

SO(N) higgs problem with adjoint+vector representations and non-linear potentials

Abstract Using the recently devised geometrical method, we analyze the quartic Higgs potential for SO(N) adjoint+vector representations. The minimum energy solutions are found to correspond to maxi-maximal little groups, but not all such groups are used. However, in the complete orbit space (including invariants not employed in the Higgs potential) we find that their strata have somewhat equal geometrical status of being low dimensional singular subspaces, i.e., cusps, edge curves, two-dimensional surfaces, etc. We also consider simple scalar potentials which are nonlinear with respect to orbit parameters and show that the directional extremum often, though not always, remains monotonic in orbit parameters within the orbit space and consequently the absolute extremum is likely to occur on the most protrudent portions of the orbit space boundary. Thus we clarify the range of validity of the Michel-Radicati conjecture and the Gell-Mann-Slansky conjecture.

Numerical computation of solar neutrino flux attenuated by the MSW mechanism

Abstract We compute the survival probability of an electron neutrino in its flight through the solar core experiencing the Mikheyev-Smirnov-Wolfenstein effect with all three neutrino species considered. We adopted a hybrid method that uses an accurate approximation formula in the non-resonance region and numerical integration in the non-adiabatic resonance region. The key of our algorithm is to use the importance sampling method for sampling the neutrino creation energy and position and to find the optimum radii to start and stop numerical integration. We further developed a parallel algorithm for a message passing parallel computer. By using an idea of job token, we have developed a dynamical load balancing mechanism which is effective under any irregular load distributions

Self-trapping nature of Tl nanoclusters on the Si(111)-7×7 surface

We have studied properties of thallium (Tl) nanoclusters formed on the Si(111)-7×7 surface at room temperature (RT) by utilizing photoemission spectroscopy (PES) and high-resolution electron-energy-loss spectroscopy (HREELS) combined with first principles calculations. Our PES data reveal that the surface states stemming from the Si substrate remain quite inert with Tl adsorption producing no Tl-induced state until saturation at Tl coverage θ=0.21 monolayers. Such a behavior, in sharp contrast with the extremely reactive surface states upon the formation of Na or Li nanoclusters, together with the presence of a unique Tl-induced loss peak in HREELS spectra suggests no strong Si–Tl bonding, and is well understood in terms of gradual filling of Si dangling bonds with increasing θ. Our calculation further indicates the presence of several metastable atomic structures of Tl nanoclusters at RT rapidly transforming from one to another faster than 1010 flippings per second. We thus conclude that the highly mobile Tl atoms form self-trapped nanoclusters within the attractive basins of the Si substrate at RT with several metastable phases. The mobile and multi-phased nature of Tl nanoclusters not only accounts for all the existing experimental observations available at present, but also provides an example of self-trapping of atoms in a nanometre-scale region.