Molecular dynamics study of gas phase and gas-surface reaction using

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Molecular dynamics study of gas phase and
gas-surface reaction using MD Trajectory
software complex
Michael Pogosbekian Valery Kovalev
Institute of Mechanics, Moscow State
University Dept. Mechanics and Mathematics,
Moscow State University
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Three levels of simulation
MD Trajectory
AVOGADRO structure
Equilibrium chemical kinetics
One-temperature approach
Non-equilibrium chemical kinetics
Two-temperature approach
Computarized handbook
Models catalogue
Level chemical kinetics
MD Trajectory
translational and vibrational temperatures
where
vibrational states of reagents and products
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Two typical cases of the nonequilibrium conditions
MD Trajectory
Boeing winged version of the Orbital Space Plane
during reentry (T gtgt Tv)
Gas discharge (T ltlt Tv)
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Software complex MD Trajectory
MD Trajectory
Triatomic collisions
vibrational relaxation
exchange reaction
dissociation
where XY Î AB, AC and P - residual atom
Tetratomic collisions
where XY and WZ - diatomic molecule Ï AB, CD,
MN - any diatomic molecule and P,Q - residual
atoms
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Collision of A atom with BC molecule
Jacobi coordinate
relative B-C motion
relative A-BC motion
ABC motion as whole
where
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Collision of A atom with BC molecule
Motion equations
where
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Definition of initial conditions
Collisions scheme
Modified parameters
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Numerical integration scheme of motion equations
MD Trajectory
Kutta-Merson method
forth order approximation automatic selection of
integration step (reduce calculation time for
10-30)
error gt ?max error lt ?min ?max ? error ?
?min
? ? / 2 ? 1.5 ? ? ?
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Random number generator uniformly distributed in
(0,1)
MD Trajectory
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Results of trajectory calculations
Reaction cross-section
Monte-Carlo method
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Results of trajectory calculations
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Potential energy surface
PES
Semiempirical methods
Generalized LEPS model
Method of diatomic complexes in molecules
Bond energy- bond order method
Ab-initio calculations
GAUSSIAN
MOLCAS
GAMESS (special version for INTEL platform - PC
GAMESS)
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Generalized LEPS model
- dissociation energy
- Morse parameter
- equilibrium distance
- adjusted Sato parameter
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Analytical representation of PES
Many-body expansion method
One-particle term
define the energy of electronically excited
atom
Two-particles term
describe the potential curve of diatomic
molecule
Three-particles term
define the interaction at close internuclear
distances
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Sorbie-Murrell function
extended Rydberg function
where
displacement from equilibrium distance
bond number
where
switching function
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Garcia-Lagana (bond-order) function
polynomial of N-th order
where
bond order coordinate
polynomial of M-th order
where
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Aguado-Paniagua function
where
l 2 or 3 for two- or three-particles term
polynomial of M-th order
where
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Features of software complex
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High performance supercomputer facilities
Moscow State University, cluster SCI - 36 CPUs
total
Node configuration Dual Pentium III/500MHz, 1Gb
RAM, 3.2 Gb HDD
Network environment SCI Fast Ethernet
Russian Academy of Sciences, cluster MVS-1000M -
768 CPUs total
Node configuration Dual Alpha 21264A/667MHz, 1Gb
RAM, 15 Gb HDD
Network environment Myrinet (2 Gb/s) Fast
Ethernet
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Parallel version of MD Trajectory
Service layer - 1 muster process
Calculation layer - N slave processes
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Data Access Layer
Three kinds of input output files
Input data fixed size rather simple structure
less than 1 Mb
Control Group describes control
function Molecule Group contains spectroscopic
characteristic of diatomic
molecules PES Group describes PES of the
investigated system
Log file dynamic size rather simple structure
less than 10 Mb
Auxiliary information which can be required for
calculation control and calculation continuation
at the next time
Result file dynamic size very complex
structure up to 100 Mb
Two ways for realization of Data Access Layer
XML files. It is realized due to LibXML2 library
XML parser and toolkit of Gnome
DataBase connectivity module for MySQL Server is
planned
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MSU cluster
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MSU cluster
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Experiment, L.B. Ibragimova
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Potential energy surface
PES for
Modified LEPS model 1
Sorbie-Murrell function 3
based on ab-initio data 2,4
Aguado-Paniagua function 4
PES for
Generalized LEPS model 1
References
1. K.J.Schmatjko and J.Wolfrum, Ber. Bunsen Phys.
Chem., 1975, 79, pp.696-707 2. P.Halvick,
J.C.Rayez, E.M.Evleth, J. Chem. Phys., 1984, 81,
pp.728-737 3. SM.Simonson, N.Markovic, S.Nordholm
and B.J.Persson, Chem. Phys., 1995, 200,
pp.141-160 4. Andersson, N.Markovic and G.Nyman,
Phys. Chem. Chem. Phys., 2000, 2, pp.613-620
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Generalized LEPS model
Equipotential contour map
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Generalized LEPS model
3D View
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Reaction cross-sections for CO(v,j)
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Comparison QCT calculations with experimental data
One-temperature rate constant
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Comparison QCT calculations with experimental data
One-temperature rate constant
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Two-temperature rate constants
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(No Transcript)
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Level rate constants
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Theoretical models for exchange reactions
? - model
Generalized Marrone-Treanor model (CVCV)
Theoretically informational model
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Comparison QCT calculations with theoretical
models
Level factor
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Comparison QCT calculations with theoretical
models
Level factor
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Comparison QCT calculations with theoretical
models
Level factor
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Comparison QCT calculations with theoretical
models
Level factor
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Further development of MD Trajectory
Investigation of Gas-Surface processes
Design of thermal protection systems in space
vehicles
Microelectronics applications
Heterogenous combustion
Main objectives
Recombination coefficient
Accomodation coefficient of chemical energy
Cite-specific effects and influence of top-layer
surface structure
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Classical molecular dynamics
Atoms are divided in two groups
1. i 1, n (gas-phase atoms)
2. k 1, N (lattice atoms)
Total hamiltonian is
The hamiltonian equations of motion are
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Definition of initial conditions
Assumptions
flat surface instead rough one
monocrystal instead polycrystal
clear surface without adsorbed layer
Detailed description of classical molecular
dynamics is represented in Gert D. Billing
Dynamics of Molecular Surface Interactions. New
York, John WileySons, 2000, chapter 6, pp.93-102
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Definition of initial conditions
For incident gas atom B
where
- randomly distributed on the surface
For adsorbed gas atom A
- randomly distributed on the surface
- the same as for atom B, where
For lattice atoms
where
- equilibrium position
- surface temperature
- force constant for atom k
- phase angle, randomly distributed in
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PES for b-cristobalite
B.P.Feuston, S.H.Garofalini Empirical three-body
potential for vitreous silica. Journal of
Chemical Physics, Vol. 89, No. 9, 1988. pp.
5818-5824
Modified form of the Born-Mayer-Huggins (BMH)
potential
where
for (
and
)
in other case.
where
- constants,
- angle subtended by
and
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Unit cell of b cristobalite lattice
Ralph W.G. Wyckoff The crystal structure of the
high temperature form of cristobalite (SiO2),
American Journal of Science, Ser.5, Vol.9, 1925,
pp.448-459
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Top layer structure of the b cristobalite
surface
M.Cacciatore, M.Rutigliano, G.D.Billing
Eley-Rideal and Lengmuir-Hinshelwod Recombination
Coefficients for Oxygen on Silica Surfaces,
Journal of Thermophysics and Heat Transfers, Vol.
13, No. 2, 1999, pp.195-203.
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Comparison of MD calculations results for SiO2
Eley-Rideal recombination probability
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Comparison of MD calculations results for SiO2
Chemical energy accomodation coefficient in the
Eley-Rideal recombination
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MD calculations results for SiO2 surface
Vibrational distribution of the formed O2
molecules in the Eley-Rideal reaction
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MD calculations results for SiO2 surface
Vibrational distribution of the formed O2
molecules in the Eley-Rideal reaction
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Fragment of crystal lattice of 3C-SiC and top
layer structure of the surface
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Comparison of MD calculations results
Eley-Rideal recombination probability
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Comparison of MD calculations results
Chemical energy accomodation coefficient in the
Eley-Rideal recombination
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MD calculations results for SiC surface
Vibrational distribution of the formed O2
molecules in the Eley-Rideal reaction
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MD calculations results for SiC surface
Vibrational distribution of the formed O2
molecules in the Eley-Rideal reaction
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Thank you for your attention