A Database of
New Zeolite-Like Materials
Michael W. Deem
Rice University
Outline
• Motivation
• Monte Carlo sampling to
construct database
• History of database of
hypotheticals
• Geometric, topological,
and physical properties
of the predicted materials
• Challenges
M. W. Deem, R. Pophale, P. A.
Cheeseman, and D. J. Earl, J. Phys.
Chem. C 113 (2009) 21353-21360.
R. Pophale, P. A. Cheeseman, and M.
W. Deem, Phys. Chem. Chem. Phys.
(2011) doi:10.1039/c0cp02255a.
Motivation & Goals
• Create database of hypothetical zeolite (SiO2) structures
• Structures should have favorable framework energies
• Screen for materials with unique properties to identify
interesting synthetic targets
– Catalysis, sorption, k∞
• Identify synthesis conditions (hard problem!)
LTL
EMT
VFI
What is a Zeolite?
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SiO2 structure
Four-connected network
3D periodic
190 known zeolites (Si1-xAlxO2)
Used for
– Catalysis, especially petroleum refining
– Gas separation
– Ion exchange
LTL
EMT
VFI
How Many Space Groups are
There?
http://cst-www.nrl.navy.mil/lattice/spcgrp/index.html
The Search Procedure
• Loop through space groups
• Loop through 3 ≤ a,b,c ≤ 30Å, dr=3Å; , , ,
d=10°
• Loop through 12 ≤  ≤ 20 T atoms/1000Å3, d = 2
• Loop through 1 ≤ nunique ≤ 8; nunique ≤ 4.5 ntot / nsymm
• Run zefsaII 100 times (solves 86% of known
structures)
• Keep structures with E < 0
• Keep best example (lowest E/atom) of each unique
topology
Monte Carlo Procedure
• For a unit cell with a given space group symmetry, tetrahedral
atom density and number of crystallographically unique
tetrahedral atoms we want to identify as many reasonable
topologies as possible
• To do this we use (many) simulated annealing Monte Carlo
simulations
The Figure of Merit
• Contains geometric and density terms
E = T T ET T  T T T ET T T   T T T E T T T 
 D ED   M EM  UC EUC
T T
T T T
T T T
Euc
• Weighting parameters selected to efficiently solve known
zeolite topologies
• Note only tetrahedral atoms included (no oxygens)
Aside: Structure Solution SSZ-77
• ZEFSA/ZEFSAII originally
developed (and still used) for
zeolite structure solution
• One can also include a match to
X-ray powder data in the figure of
merit to directly solve structures
• This approach has been effective
in solving the structures of at
least a dozen zeolites and other
layered structures to date
• SSZ-77: New high-silica zeolite
• Structure solution elucidated
synthesis conditions
– Template decomposed
– Decomposition product was
the SDA
Hypotheticals Database
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Create database of hypothetical structures
Thermodynamically accessible
Mine for structures with unique properties
Identify synthesis conditions to make
LTL
EMT
VFI
History of Database
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Roughly 2000 structures in 1992
JACS 114 (1992) 7189-7198
Compared to a few hundred in Joe V. Smith database
Produced from unit cells of known structures
Reproduced in 2003
J. Phys. Chem. B 107 (2003) 8612-8620
New search begun in 2004
Geometrical and topological features investigated
Ind. Eng. Chem. Res. 45 (2006) 5449-5454
J. Phys. Chem. C 113 (2009) 21353-21360
Phys. Chem. Chem. Phys. (2011) doi:10.1039/c0cp02255a
• Zefsa: http://www.mwdeem.rice.edu/zefsaII
Using the NSF TeraGrid
• Method is perfect for scavenging idle CPU time
• For a typical desktop processor, 1 simulated annealing run
takes on the order of minutes
• Condor is an efficient implementation of CPU scavenging at
Purdue University
• Over the last 5 years we have scavenged approx. 6 million
CPU hours from machines on the NSF TeraGrid
NSF TeraGrid Usage
• 6th biggest user of TeraGrid in 2006
• Largest user at Purdue in 2006
•
Throughput possibilities – Linux circa
2008/11. Note peaks and valleys ...
Wall Hours Delivered
Loosely Controlled Throttle. No Good Neighbor Rule.
21,801 Total Hours Delivered - 234 Hours/Hour.
Average 24 Minutes/Job. 8 Hour Moving Average.
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Other Hypothetical Databases
• See www.hypotheticalzeolites.net (an
excellent website)
• Hosts the Foster/Treacy database
• Provides links to our database, Bell/Klinowski
hypotheticals, Predicted Crystallographically
Open Database, Reticular Chemistry
Structure Resource, Euclidean Patterns in
Non-Euclidean Tilings, Jilin University
Forster/Treacy Database
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•
We are very grateful to Martin Forster and Michael Treacy for hosting our
database on www.hypotheticalzeolites.net
Forster/Treacy Database
– 933K GULP refined structures (silver)
– 333 gold structures
– Statistics
• About 3x duplicates in silver database
• Of non-duplicates, about 5% within +0.1 eV/Si on BGB forcefield (≈ +60 kJ/Si
Jackson/Catlow forcefield)
• About 30% of these are within +30 kJ/Si of quartz
• Thus, about 5,700 structures in silver database within +30 kJ/Si
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Earl/Deem database
– 4.4M unique structures
– 2.6M refined with GULP
– 1.4M within +60 kJ on SLC interatomic potential
– 330K within +30 kJ on SLC interatomic potential
Search Capability Plan
• Organize and analyze database
– Density
– Pore size
– Ring distribution
– Coordination sequence
– PXD (Le Bail’s PCOD and P2D2)
– icdd, icsd, MDI-JADE, CrystalMatch
commercial databases
Viewing the Database
• www.hypotheticalzeolites.net/DATABASE/DEEM/
Si-Only Results
• 4.37 million structures found
• As the structures produced by our Monte
Carlo annealing procedure are energetically
favorable, many have good framework
energies
Energetic Refinement Procedure
• Add O atoms between all T atoms that are connected (recall that
only T atoms are included in initial sweep of crystallographic
space)
Add O
• Use an atomistic force-field (Jackson & Catlow, 1988) and energy
minimize the structure using a Newton-Raphson procedure in the
GULP program
Energy
minimize
Refined Results
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Roughly 4 370 000 structures
3.3M unique Si-only structures
2.6M unique SiO2 structures
Two interatomic potentials used
– Polarizable SLC
– Non-polarizable BKS
• Thermodynamically accessibility
– SLC: 330k structures within +30 kJ/mol Si
– BKS: 590k structures within +65 kJ/mol Si
Interatomic Potential Anomaly
• SLC and BKS force fields
contain an anomaly: u=ae-br –c/r6
– Overlapping atoms or cores
and shells can have negative,
infinite energy
• This will result in structures with poor geometry, but
overlapping atoms, to appear to have favorable
energies
– E.g. structures with energy below α-quartz.
• This anomaly was fixed by changing the exp-6
potential to extrapolate to a large value at r=0
• Largely eliminates “too good” structures with energies
below α-quartz.
Some Structures
• From SLC database
• Structures with
energies no greater
than 30 kJ/mol Si of
α-quartz
• Typical, zeolite-like
structures
Framework Energies of Quartz
and Known Zeolites
• Most known zeolites are within 30 kJ / mol Si of the framework
energy of quartz in the SLC interatomic potential
• Of the 4.37 million topologies from the initial search, 330 000
SLC topologies have been found in this range (or better);
590 000 in BKS subset
From Foster et al., Nature
Materials 3 (2004) 234
Energy-Density Distributions
• Two major clusters of zeolite-like materials
• One group around 18 Si / 1000 A3
• One group around 8 Si / 1000 A3
SLC
BKS
Energy-Density Distributions
• SLC and BKS structures have similar
distributions
• The group around 8 Si / 1000 A3 is novel
• Corma has made structures in this range:
PNAS 107 (2010) 13997; Nature 458 (2009) 1154.
SLC
BKS
Zeolite Synthesis Mechanism
• Lie at low-density edge of zeolitelike distribution
• Probably due to current synthetic
techniques
• Mechanistic explanation of
SLC
feasability factor D. Majda et al. J.
Phys. Chem. C 112 (2008) 1040-1047
• Can the rest of the distribution be
made?
• Can the low-density structures (8
Si / 1000 A3) be made?
BKS
Ring Distributions
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Fundamental, non-decomposible rings
SLC and BKS topologies are similar
Quite a few large-membered rings
Distribution not sensitive to presence of 3-rings
SLC
BKS
Ring: Hypotheticals vs Knowns
• Reasonably good agreement between predicted
and known ring distributions
• SLC and BKS ring distributions are similar
• More large-membered rings predicted to exist
• 3-rings correlated with 9-rings in knowns, but not
in hypotheticals
SLC
BKS
Knowns
Low Energy Structures
• Structures with energy
below quartz
– Can be artifacts of
overlapping shells or
atoms in SLC or BKS
• In this version of the
database there are only
2 within -30kJ/molSi for
SLC and none within
-65kJ/molSi for BKS
High-Frequency Dielectric
Constant
• Example property calculation
• Many structures with desirable k < 1.6
Angew. Chem. Int. Ed. 45 (2006) 6329-6332
• Large rings correlated with low k
PXD Search/Match
• Structures deposited in Armel Le Bail’s PCOD
and P2D2
• Within 1% on cell parameters for knowns
• So, search/match should succeed
A. LeBail Powder Diffraction S23 (2008) 5-12
SLC
BKS
Knowns
Screening the Database
• David Sholl at Georgia Tech
– Adsorption, diffusion, geometry
• Berend Smit at Berkeley
– CO2 sequestration
• Chris Floudas at Princeton
– Geometry
• Randy Snurr Northwestern
– MOF analogs
• Catalysis
– D. Majda et al., J. Phys. Chem. C, 112 (2008) 1040, “Hypothetical Zeolitic
Frameworks: In Search of Potential Heterogeneous Catalysts”
– B. Smit & T. L. M. Maesen, Nature, 451 (2008) 671, “Towards a molecular
understanding of shape selectivity”
Big Picture Questions/Challenges
• Can we identify structures for particular applications?
– e.g. CO2 separation?
• How does one synthesize them?
– Which structures can be synthesized?
– What OSDAs can be used to make them?
• Also: solution conditions, co-templates
• Significant reason for promise