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Challenges in Multi Scale
Modeling-Our Experience in the Polymer Modeling Project-
Masao DoiDepartment of Applied Physics
University of Tokyo
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Outline
What is multi-scale modeling
The polymer modeling project Objective
The difficult part Our strategy Some outcomes
Conclusion
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What is Multi Scale Modeling
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What is multiscale modeling? A modeling which uses two or more models
for different scale
by concurrent calculation e.g. Car-Pallinello methodby separate calculation
e.g. conventional method
Multiscale calculation can be done
The core is to make consistent models bypassing information among differentsimulation programs.
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Multiscale modeling is difficultHow to let different programs share information
Some kind of translation is needed
How to gurantee the correctness of the
translation.Some uncertainities are unavoidable
How to ensure sustanable development
Some uncertainities are unavoidable
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The Polymer Modeling Project
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The Polymer Modeling Project
length cmtime sec
length nmtime psec
Seamless Zooming
Bridging micro and macroMETI project from1998 to 2002
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Mesoscale Simulation Engines
sec
msec
sec
nsec
psec
fsec
fm pm nm m mm m
Micro hydrodynami
Interfacial dynamics
Molecular dynamicsReptation dynamics
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Molecular Dynamics
Aoyagi,SawaSolve the equation ofmotion of particles:
i2i
2 Udtd
m rr
=
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Interfacial Dynamics
Honda,KawakatsuSove the Edwards equation for
polymer conformation Structure of polymers near the interface Phase separation, Microphases,
Micellization
( ) ( ) ( )r r r ,nQV6
b,nQ
t2
2
=
)]n,r (Q[V)r (V =
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Micro HydrodynamicsYamaue, Taniguchi, Sasaki
Fluid engine and solid (gel)engine.
Solve continuum equations Stokes eq. for velocity and
pressure Elastic eq. for displacement Diffusion eq. for solute and ions.
Poisson eq. for electric field
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How to Bridge Simulation Engines
sec
msec
sec
nsec
psec
fsec
fm pm nm m mm m
S i m u l a t
i o n P l a t f
o r m
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Difficulty in the design of the
simulation platformIntegration of engines requires a
common expression for physical data,but it is very difficult to set up such dataformat. Different engines use different physical
models, and need diffirent data.
The mesoscale engines are evolving, andthe platform has to accomodate theengines which will be developed in future .
Integration of engines was very very difficult.
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Open is the key
Multiscale modeling is a grand challenge.Let us try to make soft wares which willgrow and expand after our project ends.
The system should be able to grow on its own.We should not force our way of zooming: thebasic part must be independent of it.
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Our decision for the platform design
We leave the task of defining the datastructures to researchers.
We determine a rule to express the datastructure.
The platform provides a service for engineswhich state the data structure following thisrule.
We dont impose zooming.
We dont define words.
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UDF (User Definable Format)
UDF consists of two parts:
the data definition part the data part.
The definition part defines the type, unitand the other attributes for each item in
the data.The data part gives the value for eachitem.
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begin{def}oscillator: {
mass : float [kg]spring_constant : float [N/m]friction_constant : float [N*s/m] }
initial_condition:{ position: float [m]velocity: float [m/s] }
end{def}begin{data}
oscillator:{0.05, 0.01, 0.0001}
initial_condition:{-0.3, 1.0}end{data}
An example of UDF
Definition of
data structure
Data
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Unit Name Value
Script (Python)
Results
Simulation platform of Octa system
n ma on y py on program
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n=size($atom[])while n>0:n=n-1sphere($atom[n].position,0)if n>0:cylinder($atom[n].position, $atom[n-1].position, 2)
n ma on y py on program
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PASTA
COGNAC
SUSHI
MUFFIN
PASTA
Open Computational Tool for Advanced Materials
O penC omputational T ool forAdvanced material technology
Octa system
Open to public athttp:octa.jp in 2002
Has been updatedby voluntary group
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An example: study of ABAtriblock copolymers
Symmetric Triblock Polymer AxByAxxB AxA y
LamellaCylinder Sphere
What structure is formed for the tri-block copolymers.How does the bridging affects the mechanical properties.
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Results of zooming in
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Aoyagi et al. Fig.6
Equilibrium structure
A5B73A5
PS2600 IP20000 PS2600
347 polymers8 unit cell of bcc
Deformation of domains
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Deformation of domains
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Aoyagi et al. Fig.7
Stress- strain curve for spherical
structure
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3D TEM Octa
Fusion with experimental system
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Data of 3D TEMGeneral Chains
MD EnginesDensity Biased
Monte Carlo
Virtual experiments
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Virtual experiments
Similar things can be don
MechanicalThermalTransportOptical
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Conclusion
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Summing up our experience
We realized that collaboration of engines, andcollaboration of human being are more importantthan programmed zooming
We decided not to pursue automatic zooming.We focused on constructing a platform on whichvarious simulation programs can collaborate witheach other.This gave flexibility and expandability to Octa
system.ulti-scale modeling is a grand grand chanlleng