|
Abstract : Vol.38No.1(2003.3)
Special Issue：Multiscale Simulations for Materials
|
|
Review
|
|
| P.1 |
Multiscale
Simulations for Materials (Conspectus) |
| |
|
Shi-aki Hyodo
|
| |
Most material simulation studies have been previously
investigated individually by atomistic /molecular level
microscopic calculations and by characteristics-predictable
macroscopic simulations. Recently, the necessity for
relating the characteristics of materials as chemicals
with the behavior of materials as macroscopic objects
is observed. Progresses in multi-scale simulation for
cooperating spatially-temporally different calculation
methods and in meso-scale simulation for the intermediate
region between micro- and macroscopic scales are expected
to satisfy this necessity. The present paper gives a
conspectus of the background of such a necessity and
of the related calculation techniques and presents a
brief introduction to the methods appearing in the present
special issue.
|
|
Research Report
|
|
| P.10 |
Hierarchical
Procedure Bridging the Gap between Mesoscopic and Atomistic
Simulations for Materials Design |
| |
|
|
| |
A hierarchical procedure bridging the gap between atomistic
and mesoscopic simulations for materials design is presented.
A dissipative particle dynamics (DPD) is adopted for
a mesoscopic simulation technique. In this method, a
molecular structure is represented using a coarse-grained
model, connecting soft spherical particles that correspond
to a group of several atoms. The interaction parameters
of the mesoscopic model, which are related to Flory-Huggins
c-parameters, are estimated by calculating the energy
of mixing for each pair of components in the atomistic
simulation. Mesoscopic structures of the binary polymer
blend are simulated with realistic c-parameters using
DPD. This bridging method from the atomistic to the
mesoscopic level is applied to prediction of the mesoscopic
structure of a hydrated polyelectrolyte membrane for
fuel cells. The simulated structure of the membrane
and its dependence on water content are in good agreement
with experimental reports. For a reverse bridging method
for different scale simulations, the molecular structure
at the interface is extracted from the simulated mesoscopic
structure by mapping atoms to the concentration profile
of each component using a Monte Carlo technique. The
complicated morphology of the binary polymer blend is
successfully generated using this procedure. In the
case of a hydrated polyelectrolyte membrane, an atomistic
structure of a water channel is generated based on the
mesoscopic structure. It is confirmed that the number
of water molecules in the first coordination shell around
the sulfonic acid group is of the same magnitude as
the experimental study.
|
| P.17 |
Lattice
Boltzmann Method and its Application to Flow Research
Report Analysis in Porous Media |
| |
|
Hidemitsu Hayashi
|
| |
Under the existence of an external force, a lat-tice
Boltzmann method (LBM) is derived by dis-cretizing the
Boltzmann equation with respect to velocity, space and
time. The LBM is applied to simulations of flow through
three-dimensional po-rous structures of Nafion polymer
membranes. Geometry data of Nafion are constructed based
on the result of a dissipative particle dynamics simulation
for three values of water content, 10%, 20%, and 30%,
and are used as the geome-try input for the LBM. Using
Darcy's law, the permeability of the porous structure
is extracted from the results obtained by two kinds
of LBM, the LBM under an external force and the LBM
un-der a pressure gradient. The two types of LBM are
found to produce permeabilities that are in good agreement
with each other.
|
| P.26 |
Electronic
State Calculation for Hydrogen Atom under Inhomogeneous
Field |
| |
|
Shunsuke Yamakawa, Shi-aki Hyodo
|
| |
We discuss herein the effectiveness
of the Gaussian-finite element (FE) mixed basis method
for the purpose of calculating the electronic state
under an inhomogeneous electrostatic field. FE basis
functions, which possess high degrees of freedom, are
combined with Gaussian basis functions in order to describe
the steeply varying electron distribution near the nuclei.
First, this method was applied to the electronic state
calculation for a hydrogen atom without external fields.
It was shown that FE basis functions automatically expressed
the part of the wave function which can not be expressed
using only Gaussian basis functions. Secondly, the model,
in which a hydrogen atom was positioned between two
conductors, was applied in order to discuss the electronic
state of hydrogen in the grain boundary of the polycrystalline
metal. The spherical conductors and the crystal grains
were adopted as conductors of nanometer scale. The crystal
grains were extracted from the polycrystalline structure
by 3-D Phase Field simulation. The eigenvalue of the
hydrogen atom was found to depend on the diameter of
the spherical conductors when the diameter was less
than 5 nm. The wave function of the hydrogen atom was
distorted due to the complicated grain configuration.
The FE basis functions effectively represented the wave
function distorted by the existence of inhomogeneous
electrostatic fields.
|
|
Review
|
|
| P.33 |
Problems
on the Connection between Quantum and Classical Pictures
(Commentary) |
| |
|
Shi-aki Hyodo
|
| |
Computational observation of effective information
of materials related to microscopic structures and macroscopic
properties requires that the quantum mechanical picture
be described systematically and consistently with classical
physical pictures in advance. This problem is related
to what is called the problem of measurement for a quantum
mechanical system, which has been a long-standing problem
since the beginnings of quantum mechanics. Conclusion
of this problem has not yet been established as common
understandings. Brief explanations are presented here
in relating matters in multiscale simulation of materials
as well as a recently reported extrinsic method by which
to avoid such problems.
|
 |
