Molecular Dynamics Simulation of Surface Processes...

M. Rutigliano and M. CacciatoreCNR-IMIP,Via Amendola 122/D,Bari, ITALY

Molecular Dynamics Simulation of Surface Processes involving O

atoms on Silica Surfaces

1st year report meeting Barcelona, 2-3 June 2011

[email protected]


OUTLINE

Surface Processes

Molecular Dynamics Approach

Surface characterisation

• Building up of a 3D lattice crystal

• Phonon frequency distribution

O,O2-silica interaction potential determination

• DFT calculations

Semiclassical Collisional Method

Results&Discussion

O atoms adsorption on silica

O atoms recombination on silica

• Trajectory propagation


(some) Surface Processes

Inelastic processesAtom Adsorption

Dissociative chemisorption

E-R recombination

L-H recombination

• Dissociative chemisorption of diatomics and small polyatomics

• Inelastic Processes

• Atom adsorption

• Atom Recombination


Molecular Dynamics(MD) Approach

Following our approach on the dynamics of atom-molecule/surface interactions [1], we

study the O atoms recombination/adsorption dynamics on :

b-cristobalite

The approach is fully ab initio and it is carried out through two main steps:

1. DFT electronic structure calculations are performed to calculate theinteraction forces exerted between the gas-phase specie and the substrate

2. The semiclassical approach is applied to study the dynamics of the chemical processes going on at the surface

[1] G. D., Billing, (2000). Dynamics of Molecule Surface Interactions, Wiley, New York


Silica Surface

149 atoms

b-cristobalite

O-Si-O bonding angle: 109.48°

Si-O distance: 1.54Å

O-O distance: 2.54 Å

0 400 800 1200

Frequency (cm-1

)

0

5

10

15

Den

sity

of

stat

es


The Semiclassical Collisional Method

Quantum systemphonons

Classical systemgas-phase particles

Hamilton ‘s equations

TdS equations

Veff

Veff(r,R|t,TS)= <Yph(t, TS)|Vint(r,R)| Yph(t, TS)>

phSeffi

i

i

ETtRrVrVm

PH ),,,()(

2

12

,

MD Calculations


Oad * silica + Ogas ----> “products” + silica

Oad is chemisorbed on a Si atom

at the equilibrium distance of

1. 54Å from the surface and

it is in thermal equilibrium

with the surface at TS=1000K

Ogas strikes the silica surface

with polar angles ()=(0,0) respect

to the surface.

The kinetic energy of the

impinging atom is in the range

[0.004-1]eV.

O,O2/SiO2 interactionCNR-IMIP M. Rutigliano and M. CacciatoreCASPUR C. Zazza, N. Sanna, S. Orlandini


DFT RESULTS

Si

0 1 2 3 4

Distance from the surface(Å)

-6

-3

0

3

6

9

In

teracti

on

Pote

nti

al(

eV

)

Eb=5.57eV

1.0 2.0 3.0 4.0 5.0RO-O distance(Å)

-3.0

-2.0

-1.0

0.0

1.0

2.0

In

teracti

on

en

erg

y (

eV

)

Eb=2.1eV


Potential Energy Surface

1 2 3 4 5Interatomic Distance RO-O (Å)

2

3

4

5

Dis

tance fro

m t

he s

urf

ace(Å

)

-5.4 -5.2 -5.0 -4.8

-4.8

-4.6

-4.6

-4.4

-4.4

-4.3

-4.3

-4.1

-4.1

-3.9

-3.9

-3.7

-3.7

-3.5

-3.5

-3.3

-3.3

-3.1

-3.1

-2.9

-2.9

-2.7

-2.7

-2.5

-2.5

-2.3

-2.3

-2.2

-2.2

-2.0

-2.0

-1.8

-1.8

-1.6

-1.6

-1.4

-1.4

-1.2

-1.2

-1.0

-1.0

-0.8

-0.8

-0.6

-0.6

-0.4

-0.4

-0.2

-0.2

-0.1

-0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.0 2.2 2.4 2.6

2.8

3.0

rO-O

Recombination Probability


0.01 0.1 16 2 3 4 5 67 2 3 4 5 67

Kinetic Energy (eV)

0

0.01

0.02

0.03

0.04

0.05

Recom

bin

ation P

robability

Oad*SiO2+Ogas--->O2(v,j)

Energy flow pathways in recombination reaction

Hadwall + HgasH2(v;j) +Eexo

Eexo

PHONONS e/o ELECTRONS

• VIBRATIONS

• ROTATIONS

• TRASLATION

Molecular Internal states

Energetics


0.01 0.16 7 2 3 4 5 6 7 8

Kinetic Energy(eV)

0.0

0.1

0.2

0.4

0.5

0.6

Energ

y F

raction

Erot

Evib

Etr

Eph

Oad*SiO2+Ogas--->O2(v,j)

Vibrational Distributions


0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Vibrational Quantum Number

0

0.001

0.002

0.003

P(v

)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40


0

0.0005

0.001

0.001

0.002

P(v

)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40


0.0e0

2.0e-4

4.0e-4

6.0e-4

P(v

)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40


0.0e0

1.0e-4

2.0e-4

3.0e-4

4.0e-4

P(v

)

Ekin=0.006 Ekin=0.008

Ekin=0.05 Ekin=0.08

Probability for other surface processes


0.01 0.1 16 2 3 4 5 67 2 3 4 5 67

Kinetic Energy (eV)

0.4

0.6

0.8

1.0Pro

bability

Oad+Ogas

0.01 0.1 16 2 3 4 567 2 3 4 567

Kinetic Energy (eV)

0.00

0.20

0.40

0.60

Pro

bability

(O2)ad

0.01 0.1 16 2 3 4 567 2 3 4 567

Kinetic Energy (eV)

0.00

0.01

0.02

0.04

Pro

bability

Ogas+Oad

0.01 0.1 16 2 3 4 567 2 3 4 567

Kinetic Energy (eV)

0.00

0.05

0.10

0.15

Pro

bability

Ogas+Ogas

Oad*SiO2+Ogas--->…….

O atom adsorption


Ekin(eV) ADSORPTION INELASTIC

0.1 0.863 0.137

0.2 0.941 0.058

0.3 0.757 0.243

0.5 0.822 0.178

0.8 0.787 0.212

1.0 0.355 0.645

Probabilityb-cristobalite

TS=1000K

O atom adsorption: surface effect/1


b-cristobalite


0.2 0.941 0.058

0.5 0.822 0.178

0.8 0.787 0.212

b-quartz


0.2 0.652 0.348

0.5 0.648 0.351

0.8 0.635 0.365

O atom adsorption: surface effect/2


b-cristobalite

b-quartz

Ekin(eV) ADSORPTION INELASTIC PROCESSES

0.2 0.237 eV 0.373 eV

0.5 0.375 eV 0.358 eV

0.8 0.548 eV 0.478 eV

Ekin(eV) ADSORPTION INELASTIC PROCESSES

0.2 1.67 eV 0.293 eV

0.5 2.03 eV 0.579 eV

0.8 2.64 eV 0.620 eV

O,O2/SiO2 interactionCNR-IMIP M. Rutigliano and M. CacciatoreUB P. Gamallo and R. Sayós


O/b-cristobalite interaction potential/1

Surface Sites

-8

-8 -6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

8

1

X(Å)

T1

S2

H1

B1





Z=5 Å Z=2.5 Å

Z=1.4 Å Z=0.7 Å


O2/b-cristobalite interaction potential

rO-O

rO-O


O,O2/b-cristobalite: Potential Eenergy Surface

bbb ,;,,,, 2211

2

1

,,,,, )2()1(2)()2()2()2()1()1()1(rRRRRIrVRRVzyxzyxV slabOOO

i

iislabOOOOOOOT i

rO-O

RO

-O/Å

rO-O

RO

-O/Å


Future Work

Implement the new PES in the MD code

MD calculations to calculate: recombination probabilitiesadsorption probabilitiesreactions energetics

Comparison with results obtained by UB group using classicaltrajectory method

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