Journal of Computer Chemistry, Japan -International Edition
Online ISSN : 2189-048X
ISSN-L : 2189-048X
Current issue
Displaying 1-3 of 3 articles from this issue
  • Hirotaka TANIMURA, Shigeyuki TAKAGI, Tsutomu KAKUNO, Rei HASHIMOTO, Ke ...
    2022 Volume 8 Article ID: 2021-0024
    Published: 2022
    Released on J-STAGE: February 19, 2022
    Supplementary material

    We have succeeded in improving the gain of the base quantum cascade laser (QCL) through experiments and device simulations using the nonequilibrium Green’s function (NEGF) method, and we investigate the factor that increases the gain by reducing the thickness of the barrier by 10%. Specifically, we analyzed the minibands (Wannier–Stark states), density of states (DOS), and electron density that contribute to the emission. The results show that the gain enhancement is due to the increase in the electron density of the quantum wells in the active region and the increase in the oscillator strength between the minibands that contribute to the emission. Quantum mechanical calculation like the NEGF method is very effective for mesoscopic systems such as the active layer of QCL.

  • Yoshimitsu ASAKURA, Daisuke KUWAHARA, Naoya NAKAGAWA
    2022 Volume 8 Article ID: 2021-0048
    Published: 2022
    Released on J-STAGE: April 22, 2022
    Supplementary material

    The NMR chemical shifts for metal ions in aqueous solutions of inorganic salts often change with the solution concentration. These changes are referred to herein as dilution–concentration (dc) shifts. For main-group elements, the dc shifts generally increase with increasing atomic number. We calculated the dc shifts for various metal and nonmetal ions in aqueous nitrate solutions of elements in periods 5 and 6 by the DFT method based on the spin–orbit ZORA Hamiltonian. The calculation results revealed that the dc shifts of metal and nonmetal ions with the outermost shell electron configuration of 6s2 are primarily determined by the changes in the spin–orbit interaction terms of the shielding constants. Furthermore, the spin densities of the Pb(II) ions in aqueous lead nitrate solutions under an external magnetic field were calculated using the matrix/modified Dirac–Kohn–Sham Hamiltonian, which confirmed the presence of Fermi contacts between the spin-polarized electrons and the lead nucleus. When a suitable threshold for visualizing the spin density was set, there was no Fermi contact in the infinite dilution state, whereas the upward-spin electron was in Fermi contact with the lead nucleus in the saturation state. There have been few reports of the NMR chemical shifts of heavy atoms in terms of Fermi contacts with relativistically spin-polarized electrons. We succeeded in clarifying how the dc shifts occur on the hydrated ions of heavy atoms by visualizing the Fermi contact of spin-polarized electrons with heavy-metal nuclei.

  • Mizuho YOKOI, Masayuki KAWAURA, Yuta ASANO, Qian CHEN, Yusuke OOTANI, ...
    2022 Volume 8 Article ID: 2022-0009
    Published: 2022
    Released on J-STAGE: September 23, 2022

    In this work, we performed reactive molecular dynamics-based sliding simulations of diamond-like carbon/Fe in the presence of H2O and O2 molecules to analyze tribochemical reaction processes and the atomic-scale wear mechanism. The atomic-scale wear amount in the O2 environment model is smaller than that in the H2O environment model. H2O molecules adsorbed on the surface prevent adhesion between surfaces. However, they are ejected from the contact surface when the high contact pressure was applied, allowing the direct convex-to-convex contact. On the other hand, O2 molecules reacted with the Fe surface, forming a chemically inert oxide layer, thereby leading to preventing atomic-scale adhesive wear.