Rasoul Nasiri

Public Presentation at University of Brighton, UK, October 17th, 2012

Ab initio molecular dynamics simulation of the

evaporation process in droplets

Outline

Evaporation Molecular Modeling for Fuel Droplets:

Why and How?

Quantum Chemistry Effects During the Evaporation: Quantum Chemistry Potentials against to Classical Force Fields

Effective Methodologies for Observing of these Effects:

Ab initio MD Simulation

Hybrid Methods QM/MM

Implicit/Explicit Models

Advantages and Drawbacks over the Methods

Proposed Strategy

Why Molecular Modeling?

Kinetics, Hydrodynamics and Transition State Theory

~10-9m ~10-6m

~10-9m ~10-6m

Fuel Gas-Droplet systems are very elaborate

Required Approaches with different resolutions Molecular Modeling as well as Kinetics and Hydrodynamics

Computational chemistryEvaporation Coefficient (How)?

Ref: Xie, J.-F., Sazhin, S.S. and Cao, B.-Y.,

Journal of Thermal Science and Technology.

2012, Vol. 7, No. 1, 2012

How?

MD Simulation with Classical Force Fields or Quantum Chemistry Potentials?

Quantum Chemistry Effects During the Evaporation

Different Paths and so Different Properties? Why?

What are the difference between them?

Classical

FFs

Quantum

Potentials

Energy

Position

Quantum Chemistry Effects During the Evaporation

2

612

ij

ij

ij

ij

ijnonbon

r

R

r

RU

torsionsall

nK cos1

bondsall

b bbK2

02

1

anglesall

K2

02

1

bonU

Quantum Chemistry Effects During the Evaporation

In Classical MD, No explicit Electronic Effects

Those can be Significant in the Fuel Droplet System

Due to Extreme Conditions in Combustion Chamber

Uncertainty in Estimation of the Properties,

Then Need for Improved Method

Effective Methodologies for Observing of these Effects

Ab initio MD simulation using Fragment Molecular Orbital (FMO) methodology

Divide the system into fragments

Do ab initio calculations on fragments and their n- mers

Time of Computations dramatically will decrees (from ̴ N3-4 NlogN)

Hybrid Methods QC/MM

Effective Methodologies for Observing of these Effects

QC Layer (External Area of Droplet)

MM Layer (Internal Part of Droplet)

Implicit/Explicit Strategy with QC Potentials

Internal part (Hydrocarbon Molecules)

External part (Implicit solvation Models)

Effective Methodologies for Observing of these Effects

Solvation Model? Number of Molecules?

Advantages and Disadvantages

Advantages:

Reduce of Computational Costs

Similarity in the Methods: Dynamics of Local Density of Electronic States (LDES) but with Different Strategies

FMO-MD: LDES is extended up to ~ 105atoms

QC/MM: LDES is focused up to ~103 atoms

Implicit/Explicit: LDES can be considered on ~102 atoms

Advantages and Disadvantages

Disadvantages:

FMO-MD: Required time of the supercomputer machine

QC-MM: - Practical Issue Selection of Boundary of QC and MM parts would be challenging

- Change in size of QC part Different values of Energy

Implicit-Explicit:

Need to be validated with LARGER systems and experimental data

Advantages and Disadvantages

Proposed strategy:

FMO-MD and Implicit-Explicit Models can be complementary

Implicit-Explicit ΔGsol as a Criteria for Residential time of Molecule in Droplet

FMO Determination of same Quantity in a more Real System

Comparison of Implicit-Explicit and FMO models with Experimental Data

Estimation of the Optimal Size of Droplet for Modeling

FMO-MD or DRC for Studying of Dynamics Evaporation Coefficient

Ref: Honnery D et al. Fuel (2012), In Press

Experimental Data

Thanks for

Your Attention

Suggestion

and Question?