Computer Modeling of Chemical Systems

Piti Treesukol

Molecular/Ionic Species• Define initial structure• Define charge/multiplicity• Method/Basis set

Optimized structure Obrbitals/Charge density Vibrational Frequency Energy Thermodynamic properties

H2O (0 1) H3O+ (1 1)

CH3COOH (0 1) CH3COO– (1 1)

Reaction

E(H2O)

E(CH3OOH)

E(H2O+CH3OOH)

E(H3O++CH3OO–)

E(H3O+)

E(CH3OO–)

Adsorption

Desorption

Proton transfer

ActivationEnergy 2Binding

Energy ProtonationEnergy

Energy Profile• Energy level diagram

CH3COOH + H2O

CH3COOH + H2O

CH3COO– + H3O+

CH3COO– + H3O+

Binding Energy

Transition state 2

Transition state 1

Transition state 3

Common Reactions• Substitution• Addition• Abstraction

ZSM-5 zeolite• 3D-crystalline structure

XYZ Coordinate

Straight Channel

ZigZagChannel

ZSM-5

H-ZSM-5/H2O

Cluster Model Tailoring

Cluster Model of H-ZSM-5

Terminatedatoms

Boundary Atoms can be fixed to mimic the crystal contraints.

Acidic Zeolite• Acidity

OH-Bond length Protonation energy

Effect of framework Effect of composition

(Si/Al) Effect of proton density

Location of Al ? Location of H ?

Transition State• H3O+ + H2O

Basis Set Superposition Error (BSSE)

• E(H3O+/small)

• E(H3O+/big)