Screening for New Materials Quantum Mechanical Computations Ghanshyam Pilania, Chenchen Wang,

1. Screening for New Materials Quantum Mechanical Computations Ghanshyam Pilania, Chenchen Wang, Chun-Sheng Liu, Vinit Sharma, Rampi Ramprasad University of Connecticut ONR Capacitor Materials Program Review March 7, 2012

2. Three Directions/Sub-projects Screening for new materials Exploration of the polymer chemical space High-throughput DFT calculations QSPR – Polymer Informatics Parallel synthesis work Ramprasad, Breneman, Sotzing Morphology & functionalization Morphology predictions Optimization of PP-OH polymers The role of OH functional groups Processing & characterization Kumar, Chung, Weiss (& Boggs, Ramprasad) Breakdown & aging Intrinsic breakdown Role of extrinsic factors (defects, disorder) Aging Multi-scale & statistical treatment Boggs, Ramprasad (& Kumar, Weiss)

3. OBJECTIVE • Given a polymer, compute the dielectric constant1 and band gap2 rapidly and accurately from first principles • Screen a large number of known and unknown polymers, and identify promising systems 1Baroni et al, RMP 73, 515 (2001) 2Krukau et al, JCP 125, 224106 (2006)

4. TECHNICAL APPROACH • Density functional theory, including van der Waals interactions and hybrid functionals • High-throughput computing for large scale screening • Evolutionary algorithms for optimal structure predictions • Cluster expansions for “mining” knowledge from data

5. van der Waals (vdW) Interactions • Polymer interchain interactions are controlled by vdW forces • Conventional DFT fails to capture vdW interactions • Lattice parameters, volumes and densities predicted incorrectly • Errors carry over to dielectric constants

6. vdW Interactions in DFT • We consider 10 polymers for which reliable crystallographic information is available • Conventional DFT functionals (LDA, PBE) • vdW-augmented functionals (PBE+vdWD2, PBE+vdWTS)1,2 • Assessment of functionals based on geometry predictions 1Grimme, J. Comp. Chem. 27, 1787 (2006) 2Tkatchenko & Scheffler, PRL 102, 073005 (2009)

7. Predictions of Geometry

8. The Assessment

9. Initial Polymer Sub-family • We assume orthorhombic crystal structure, and include vdW interactions • -XY2- homopolymers (9 systems) • -[(CH2)2-(XY2)2]- heteropolymers (12 systems)

10. Dielectric Constant Ge-F Stretching Mode F-Ge-F Wagging Mode GeF2 based heteropolymers are attractive

11. An Alternate Fast Method • Estimation of crystal dielectric constant from single-chain computations • Amenable to “high-throughput” computations

12. High-Throughput Screening • Automated “high-throughput” search via chain approach • “1stRound”: common polymers • “2ndRound”: -XY2- blocks (X = C, Si, Ge, Sn; Y = H, F, Cl, CH3, CF3) • “3rdRound”: -CH2-, -NH-, -CO-, C6H4-, -C4H2S-, -O- blocks

13. “1st Round” Results First Round: different common polymers polyacetylene, PMMA, PEEK, polycarbonate, etc.

14. “2nd Round” Results Second Round building blocks: -XY2- (X=C, Si, Ge, Sn and Y=H, F, Cl, CH3, CF3)

15. “3rd Round” Results Third Round building blocks: -CH2-, -NH-, -CO-, -C6H4-, -C4H2S-, -CS-, -O-

16. All High-Throughput Results First Round: different common polymers, polyacetylene, PMMA, PEEK, polycarbonate, etc. Second Round building blocks: -XY2- (X=C, Si, Ge, Sn and Y=H, F, Cl, CH3, CF3) Third Round building blocks: -CH2-, -NH-, -CO-, -C6H4-, -C4H2S-, -CS-, -O- εelec ~ 1/Egap Take home messages: (1) If we rely on the electronic part of the dielectric constant, we are limited by the above “universal” relationship; (2) Exploiting ionic/orientational part will require Ge or clever use of functional groups

17. A Precedent Migration of transistor technology … … from SiO2 dielectric to HfO2-based “high-k” dielectric

18. From Data to Knowledge • Mining the high-throughput data • Cluster expansion • Any property can be written as a series involving on-site, 2-body, 3-body, etc., terms • QSPR • Provides chemical intuition as to which units may be beneficial

19. Cluster Expansion (y-axis) vs DFT (x-axis) Dielectric constant (electronic) Dielectric constant (total) Band gap (eV) 2nd round systems Dielectric constant (electronic) Dielectric constant (total) Band gap (eV) 3rd round systems

20. CONCLUSIONS • Computational framework is in place to determine dielectric constant, band gap, and optimal structure • Data  knowledge (e.g., via cluster expansion or QSPR) • [QSPR explored by Breneman] • Based on the screening performed to date, polymers containing the following groups are promising: • CH2 and GeF2 units (for large electronic & ionic dielectric constant) • NH, CO, O, C4H2S, C6H4 (for large electronic dielectric constant) • [Synthesis explored by Sotzing]

21. CURRENT AND FUTURE WORK • Significantly extend the chemical space exploration • Data  knowledge (e.g., via cluster expansion or QSPR) • Further explore the identified systems, in terms of stability and morphology • Contribute to an understanding of aging & breakdown

22. RECENT PUBLICATIONS, PATENTS, AWARDS • “Dielectric Properties of Carbon, Silicon and Germanium Based Polymers: A First • Principles Study”, submitted to Phys. Rev. B • C. C. Wang, G. Pilania, C. S. Liu and R. Ramprasad • “How critical are the van der Waals interactions in polymers?”, submitted to J. Phys. Chem. C • C. S. Liu, G. Pilania, C. C. Wang and R. Ramprasad • “First principles calculations of intrinsic breakdown modeling in crystalline polymers”, submitted to IEEE • Y. Sun, S. Boggs and R. Ramprasad

23. NAVY RELEVANCE and IMPACT The polymer chemical space is explored in a comprehensive manner for the first time This effort will provide intuition and guidance for materials design for navy capacitor applications The results may also impact dielectric design and development for electronics and electrochemistry

24. NAVY RELEVANCE and IMPACT

25. Stability: Optimal Structure Prediction Oganov A.R., Glass C.W. (2006). Crystal structure prediction using evolutionary algorithms: principles and applications. J. Chem. Phys. 124, art. 244704 CY2, SiY2 GeY2 Ge favors bridging halogens (consistent with experiments)

26. Structure vs Properties Systems with bridging halogens display large dielectric constant and large band gap

27. CH2-GeF2 A sampling of low energy structures Ge-C-Ge-C (-0.08 eV) Ge-Ge-C-C (0.00 eV) “Hybrid”(-0.11 eV) Ge-C-Ge-C (-0.09 eV)