NANIWA-series

NANIWA series is a computational code for performing first principles quantum dynamics calculations. As the description implies, it is a quantum mechanical version of classical molecular dynamics (MD) calculations. A classical description of the system involved in, e.g., surface reactions (dissociative scattering, molecular scattering, dissociative adsorption, associative desorption, etc.) can be used, when quantum effects, such as tunneling, diffractions, and electronic excitations, play no essential role in the dynamics. In addition to this, the kinetic energy of, e.g., the impinging particle must be large enough, to ensure that the de Broglie wavelength is much smaller than the lattice constant of the solid (typically of the order of a few Angstroms), to be able to neglect interference phenomena. For hydrogen, with a translational energy of say 20 meV, the de Broglie wavelength is a few Angstroms. This dictates that we treat hydrogen as a quantum particle!  For all the relevant surface reactions, there is a strong interaction between the impinging particle and the surface. This compounds the situation because interactions imply coupling between the internal degrees-of-freedom (e.g., vibration, rotation, and translation) of the particles immediately involved in the reaction. The vibrational motion, e.g., requires a quantum description, esp., when the respective quanta are large. Thus, the coupling between the internal degrees-of-freedom also requires a quantum mechanical description.   As one would expect, this computation code could also handle such problems as quantum transport, and quantum scattering in general.

For the first principles quantum dynamics calculation done by NANIWA series can be broken down into two main stages, viz.,

1) Determination of the effective potential energy (hyper-) surface (PES) governing the reaction, based on the density functional theory [1].
2) Solution of the corresponding multi-dimensional Schrodinger equation for the reaction described by the above-determined PES,
    based on the coupled-channel method [2,3] and the concept of a local reflection matrix [4].


[1] P. Hohenberg, W. Kohn, Phys. Rev. 136 (1964) B864.
[2] W. Brenig, H. Kasai, Surf. Sci. 213 (1989) 170.
[3] H. Kasai, A. Okiji, Prog. Theor. Phys. Suppl. 106 (1991) 341.
[4] W. Brenig, T. Brunner, A. Gross, R. Russ, Z. Phys. B93 (1993) 91.


(To be continued.) For more details regarding the code, please contact: cmd [atmark] dyn.ap.eng.osaka-u.ac.jp.