A Database of New Zeolite-Like Materials

Michael W. DeemRice 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?• 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; , ,

d10° • 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

• Weighting parameters selected to efficiently solve known zeolite topologies

• Note only tetrahedral atoms included (no oxygens)

TTTTTTTTTTTTTTTT EEEE UCUCMMDD EEE

TT TTT

TTT Euc

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• Create database of hypothetical structures• Thermodynamically accessible• Mine for structures with unique properties• Identify synthesis conditions to make

LTL EMT VFI

History of Database

• 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

Wall Hours DeliveredLoosely Controlled Throttle. No Good Neighbor Rule.

21,801 Total Hours Delivered - 234 Hours/Hour.Average 24 Minutes/Job. 8 Hour Moving Average.

0

100

200

300

400

500

600

700

Date

Ho

urs

Del

iver

ed

• Throughput possibilities – Linux circa 2008/11. Note peaks and valleys ...

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• 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

• 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

• Add O atoms between all T atoms that are connected (recall that only T atoms are included in initial sweep of crystallographic space)

• Use an atomistic force-field (Jackson & Catlow, 1988) and energy minimize the structure using a Newton-Raphson procedure in the GULP program

Energetic Refinement Procedure

Add O

Energy minimize

Refined Results

• 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 zeolite-

like distribution• Probably due to current synthetic

techniques• Mechanistic explanation of

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?

SLC

BKS

Ring Distributions

• 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

KnownsBKSSLC

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