DEVELOPMENT OF INTERATOMIC POTENTIALS WITH APPLICATIONS TO NANOSCALE SURFACE SCIENCE By ANDREW ANTONY A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2017 © 2017 Andrew Antony To the metallurgists who inspire me most: Dad, Uncle Mike, and my late grandfather, Ken Antony (Grandpa) ACKNOWLEDGMENTS First and foremost, I would like to express a heartfelt appreciation toward my parents who have provided unconditional love and support throughout my academic career. They are wonderful people and I hope that the hard work put into this dissertation reflects the dedication and sacrifices they have made for me throughout my life. In addition, I want to acknowledge three people who have been most influential in my decision to study materials science and engineering: my father, his twin brother (my uncle), and my late grandfather. Being surrounded by metallurgists my whole life had a tremendous impact on my appreciation for engineering and critical scientific inquiry. While a researcher in California, my grandfather began taking foreign language courses as an admission requirement to graduate school. When he and my grandmother realized they would be raising twins, my grandfather ended his pursuit of a doctoral degree to take care of his family. This dissertation is dedicated to him. I am sincerely appreciative for my advisor, Dr. Sinnott, and coadvisor, and Dr. Phillpot, for leading a research group that fostered academic excellence, created strong interpersonal relationships, and stimulated intellectual creativity. The dedication and care they put into mentoring all students and researchers has made graduate school an incredible life experience for me. Dr. Sinnott exemplifies collegial professionalism and her guidance has been instrumental in helping me through a time of uncertainty as a young researcher. Our countless discussions on career choices, scientific research, and professional involvement have been paramount in helping me discover my own aspirations. I would also like to thank Dr. Richard Hennig for his scientific expertise and useful discussions while I was studying at UF. 4 A huge thank you is also extended to the research group at UF, Florida Laboratory for Advanced Materials and Simulations (FLAMES). The people in this group are incredible individuals and their intellectual support and friendship have followed me even after moving to Penn State. I am forever grateful particularly for Dr. Tao Liang whose expertise in atomic materials theory has helped me develop a mindset structured by logical and practical science. Ironically, the research I was working on as a student at UF was a collaborative project with a chemical engineering group at Penn State. Dr. Michael Janik and Sneha Akhade both provided significant contributions to our scientific work and immediately welcomed me into the Penn State community after I moved from UF to Penn State. Many thanks to both for being encouraging researchers and friends. I want to thank all my classmates and friends at UF with whom I have shared courses, class projects, and countless memories in Gainesville and Florida. In addition, I thank all the members of the racquetball clubs at UF and Penn State for their support and camaraderie while I was in graduate school. Although I moved away from my home state of Louisiana, my two brothers continued to support and motivate me, and even visited me at both UF and Penn State. We are a close-knit brotherhood and I thank them for everything they have done for me. Finally, I want to thank my girlfriend, Casey Phifer, for her never-ending support and companionship. She has stuck with me while we were both researching at schools a country apart and words alone cannot express how much I love her and cherish our relationship. 5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 8 LIST OF FIGURES .......................................................................................................... 9 LIST OF ABBREVIATIONS ........................................................................................... 11 ABSTRACT ................................................................................................................... 12 CHAPTER 1 INTRODUCTION .................................................................................................... 14 1.1 Electrochemical Systems .................................................................................. 14 1.2 Nanoscale Water-Metal Interactions ................................................................. 15 1.3 Platinum Catalysts ............................................................................................ 16 1.4 Objectives and Outline ...................................................................................... 17 2 COMPUTATIONAL METHODOLOGIES ................................................................ 21 2.1 Overview ........................................................................................................... 21 2.2 Empirical Interatomic Potentials ........................................................................ 22 2.2.1 Many-Body Potentials .............................................................................. 23 2.2.2 Charge Optimized Many Body (COMB) Reactive Potential ..................... 24 2.2.2.1 Charge- and distance-dependent interactions ............................... 25 2.2.2.2 Distance-dependent interactions .................................................... 30 2.2.2.3 Charge equilibration scheme ......................................................... 31 2.2.2.4 Electrochemical modeling developments ....................................... 32 2.2.2.5 Parameterization of COMB3 .......................................................... 33 2.3 Molecular Dynamics (MD) ................................................................................. 35 2.4 Geometry Optimization and Energy Minimization ............................................. 37 3 COMB3 POTENTIAL FOR PLATINUM METAL AND Pt/O/H INTERACTIONS ...... 40 3.1 Interatomic Potential Developments ................................................................. 40 3.2 Parameterization of Pt Metal ............................................................................. 42 3.2.1 γ Surface Energies .................................................................................. 43 3.2.2 Tensile Test Simulation ........................................................................... 44 3.3 Parameterization of Pt/O Interactions ............................................................... 45 3.4 Parameterization of Pt/H and Pt/O/H Interactions ............................................. 47 6 4 PLATINUM AND GOLD NANOPARTICLES ........................................................... 59 4.1 Metal Nanoparticles .......................................................................................... 59 4.2 Wulff-Constructed Nanoparticles ...................................................................... 59 4.3 High Temperature Nanoparticle Simulations .................................................... 60 4.3.1 Shape Change of Nanoparticles at Elevated Temperatures .................... 61 4.3.2 Diffusion of Nanoparticle Surface Atoms ................................................. 64 5 SURFACE PHENOMENA ON PLATINUM METAL SURFACES ............................ 74 5.1 Overview of Adsorption on Pt ........................................................................... 74 5.2 O* and H* Adsorption on Pt(111) ...................................................................... 76 5.3 OH* and H2O* adsorption on Pt(111) ................................................................ 77 5.4 Interfacial Molecular Ordering of Multilayer H2O on Pt(111) ............................. 79 5.5 Summary of COMB3 Pt/O/H ............................................................................. 83 6 DYNAMIC SIMULATIONS OF WATER/METAL INTERFACES .............................. 91 6.1 Overview of Cu/H2O Interfaces ......................................................................... 91 6.2 DFT Calculations of H2O on Cu(111) ................................................................ 93 6.3 COMB3 Water .................................................................................................. 94 6.4 Water Adsorption on Cu(111) ........................................................................... 97 6.5 Dynamic Simulations of Water on Copper Surfaces ......................................... 99 6.5.1 Spreading Mechanism of a Water Droplet on Cu .................................. 101 6.5.2 Effect of Surface Chemistry on Spreading Rate .................................... 105 6.6 Electrochemical Simulations of Cu/H2O Systems ........................................... 108 6.7 COMB3 Cu/H2O Synopsis .............................................................................. 112 7 CONCLUSIONS ................................................................................................... 130 APPENDIX: POTENTIAL PARAMETERS FOR Pt-O-H COMB3 POTENTIAL ........... 133 LIST OF REFERENCES 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