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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