Using the Effective Fragment
INTRODUCTION Potential Method in Atomistic • There is good agreement between
T8 and D4 energies
Simulation of CO2 adsorption in 590
Zeolites are three dimensional aluminosilicates which can be used as
catalysts, ion exchangers and molecular sieves. The possibility of using zeolites
to separate CO2 from other gases has important implications in CO2 removal
from the atmosphere. Adsorption of CO2 in silica zeolites (Silicalite, ITQ3 and Felix Amankona-Diawuo and Daniela Kohen 390
ITQ7) have been studied using Classical Molecular Dynamics (MD) and Grand Carleton College
Canonical Monte Carlo (GCMC) simulations which utilized classical force fields to
model atoms as charged Lennard-Jones centers. Mark S Gordon 290 cube
Iowa State University
Interaction Energy (kcal mol-1)
EFP EXTENSION TO ZEOLITES: PROOF OF -8.2 -6.2 -4.2 -2.2
ITQ7 with molecular formula Si64O128 Comparison of Potential enerfgy surface for T8 and D4.
• A preliminary study on the energy of CO /zeolite system and 2 800
Our adsorption values obtained from simulation were in good agreement with x bv
barrier to insertion of the CO2 into the zeolite was done to determine EFP energies are
experimental values for Silicalite. whether EFP could be used to adequately describe the system. higher than MP2 700
energies but lower
Amount adsorbed CO
simulation • A small piece of the zeolite T8 was used since calculation on whole than Classical 600
(mol/kg) 3.5 zeolite is time consuming energies
3 • The barrier to insertion was determined by calculating single point 500
2.5 energies at various position of CO2 during the insertion into the T8 Classical
Energy (kcal mo
2 CO 2
• For the barrier of insertion, it has been shown that only the 300
interaction with the surface of insertion is important and therefore
1 the rest of the T8 can be ignored. MP2 energies were calculated
0.5 using the surface, D4 for comparison with the EFP energies. 100
• Energy calculations were also done using the classical force fields
0 5 10 15 20 0
P for comparison with EFP and MP2.
(bar) -4 -3 -2 -1 0 1 2 3 4
Isotherm showing adorption of CO2 and N₂ in silicalite -100
ITQ7 unit cell
Comparison of EFP, MP2 and Classical energies for D4
To improve the accuracy of our results, we are hoping to employ a Quantum
mechanically based description of the system. Full ab initio is practically
impossible but we are interested in employing the quantum mechanically
based Effective Fragment Potential (EFP) method to model the system.
• From the high energy barrier determined, it can be concluded that the T8 sites
EFFECTIVE FRAGMENTS POTENTIAL (EFP) in ITQ7 are unfavorable sites for CO2 adsorption. This is consistent with previous
study which showed that CO2 was indeed very unlikely to be found at the T8 sites
METHOD T8 as shown below
ITQ7 unit cell, T8 and D4 structures.
EFP is a Perturbation theory applied to non-interacting Fragments.
• All calculations were done using GAMESS Electronic Structure Code
Standard Ab Inition Calculation Effective Fragment Potential Calculation
T8 site is
E = Eab inition + Einteraction ITQ7 structure showing T8 cite
690 • T8 is smallest channel in ITQ7 but for larger channels down z-axis
EFP is expected to be
Einteraction = Ecoulomb + Epolarization + Edispersion + more accurate.
Eexchange-repulsion + Echarge-transfer 590
• The expansion in actual zeolite due to insertion of CO is negligible due to the
down x-axis down y-axis 2
rigid and crystalline framework of zeolite. Therefore thedown x-axisinternal y-axis
Features of EFP 490
coordinates of EFP should give good results.
• Polarizable force field 390 • We have reason to be hopeful about EFP!
• All EFP force field parameters are obtained from a separate ab
initio calculation: no fitted parameters
• Computationally cheap 190
• Study insertion of CO2 into larger channels in the zeolite.
Interaction Energy (kcal mol
• Covers all major types of intermolecular forces Bottom half of T8 Top half of T8
• Accuracy of EFP can be systematically improved • In our classical MD and GCMC simulations, interaction between zeolites
-10 and adsorbate species are precomputed and stored into a grid to save
• In present implementation, accuracy of EFP is - 8 .2 - 6 .2 - 4 .2 - 2 .2
d is t ( a n g s )
- 0 .2 1 .8
similar to accuracy of MP2 PES using EFP for CO2 insertion into T8 -Develop a grid using EFP
• Doesn’t allow geometry relaxation in each interacting fragment
no conformational freedom
Uses of EFP ACKNOWLEDGEMENTS
• Solvations • The Energy barrier using EFP and MP2/ 6-31+G(d) were determined to Thanks to:
• Mark Gordon, Lyuda Slipchenko, Dan Kemp, Mike Schmidt and Entire Gordon
• Heterogeneous catalysis be 610.45 kcal mol-1 and 342.17 kcal mol-1 respectively.
Group and Iowa State University
• Enzyme activity • Daniela Kohen and David Selassie from Carleton College
• PRF and Carleton College for Funding