Professor of Physics Dr Wai-Yim Ching has led his current research group for over 35 years. In this enlightening interview, he describes how computational advances have maintained his interest in materials science and his revolutionary method to derive electronic structure

Can you provide an overview of your academic background and explain what initially attracted you to materials science?

I was trained as a solid-state theorist at Louisiana State University, USA. I then spent four highly productive years at the University of Wisconsin-Madison as a postdoc, where I worked on the electronic structure of amorphous materials and theory of magnetism. This greatly broadened my research interests. When I secured my first faculty position at the University of Missouri-Kansas City (UMKC), I continued exploring different crystalline and non-crystalline materials, but I was fairly isolated, having limited interaction with experimentalists. This completely changed when I spent a sabbatical year at the Max Planck Institute for Metals Research in Germany, where I met prominent materials scientists from all over the world and established many collaborations, many of which I maintain to this day.

What makes density functional theory (DFT) such an important method for your work?

DFT is one of the most successful theories of the past half century in physics and chemistry. It puts one-electron theory on firm theoretical

ground, enabling the prediction of materials properties, fuelled by unprecedented advances in computing. As a graduate student, I was using a deck of punch cards on an IBM System/360 machine to do calculations, whereas today I routinely use petascale supercomputers. With exascale computers on the horizon, I am excited about the future of computational materials science.

Since 1978, you have led the Electronic Structure Group (ESG) at UMKC. What are the main aims of ESG and are there any specific developments you would like to highlight?

The main achievement of ESG is the development of a robust electronic structure technique – the orthogonalised linear combination of atomic orbitals (OLCAO) method. I conceived OLCAO at the University of Wisconsin-Madison and over the years it has been steadily improved and refined, making it extremely competitive. Around 10 years ago, my colleague Professor Paul Rulis rewrote the OLCAO code to make it a very efficient computational package. This enabled us to conduct calculations relatively easily on some very complex systems, including biomolecular materials. We continue to develop and improve the OLCAO method today, applying it to different materials systems.

Why did you choose to conduct research into the electronic structure of a collagen molecule recently?

I started work on models of collagen molecules around 10 years ago to test the applicability of OLCAO. This research was revived recently when I became a member of a large collaborative project led by Professor Roger French entitled ‘Long Range van der Waals-London Dispersion Interactions for Biomolecular and Inorganic Nanoscale Assembly’, supported by the US Department of Energy-Basic Energy Sciences.

Theoretical computation of the electronic structure, charge distribution and optical

properties of complex biomolecular systems and inorganic nanoscale materials is an important component of this project. Collagen is of great importance in biomedicine and polymer science, but other biomaterials currently being investigated include DNA, peptides and large proteins, as well as their interaction under different environments.

Throughout your academic career, you have worked alongside a range of institutions and experts. How important is collaboration to your studies and to innovative research generally?

I have gained new knowledge, creative ideas, clever tricks, novel techniques and different perspectives on research from my mentors, colleagues, collaborators and students. Without such collaborations, little innovation can be achieved. I have also learned that collaborations require a lot of patience, persistence, mutual respect, understanding and appreciation, and of course hard work. My research is the product of many such fruitful collaborations.

Your investigations often span different disciplines. Has this crossover in traditional boundaries impacted your studies and do you think a multidisciplinary approach is advantageous within the physical sciences?

Although trained as a condensed matter theorist, I consider myself simply a physical scientist, working in many overlapping disciplines including condensed matter physics, chemistry, crystallography, materials science, engineering, biomedicine, pharmacology, geoscience and computer science. This has greatly broadened both the vision and scope of my research. I think that a multidisciplinary approach is advantageous to physics and other disciplines, and truly believe that the boundaries of these seemingly distinctive academic disciplines are vanishing fast.

Where theory, simulation and experiment meet

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Revealing material structureA longstanding research group at the University of Missouri-Kansas City, USA, is tackling some of the biggest challenges in computational biophysics. The team has revealed the atomic-scale electronic structure of large proteins and developed methods in high demand in biophysics

ADVANCES IN MOLECULAR biology and bioinspired materials are rapidly revealing the structures of very complex proteins, but precise details remain elusive in many cases. However, modelling biological systems through computational techniques can aid in describing the atomic-level physics of proteins and other biomolecular structures like DNA molecules.

The introduction of density functional theory (DFT) and a raft of computational methods that accompanied it have revolutionised the fi eld, advancing quantum proteomics and rational drug design. Yet, the majority of studies at this level still involve relatively small molecules – making them inadequate for investigating large proteins which can comprise several hundreds of amino acids. So, despite the huge progress made in recent decades, it remains a signifi cant challenge to address large, complex biomolecular systems.

SIFTING THROUGH COMPLEXITY

For over 35 years, Dr Wai-Yim Ching, Professor at the University of Missouri-Kansas City, has led the Electronic Structure Group (ESG), which researches the electronic, optical, structural, dynamic, magnetic and superconducting properties of a variety of materials.

Ching hopes to meet the challenge of modelling complex systems in different confi gurations and environments, using novel computational approaches to describe mesoscale interactions. He also wishes to shed new light on the dynamics of biophysical systems. While the majority of research in this area uses methods based on empirical force fi eld models to study the dynamics of biomolecules, ESG places focus

on the fi ner details, such as electronic structure, charge distribution and interatomic bonding.

AN EVER-EVOLVING METHOD

Many years ago, Ching developed a computational method to calculate the electronic structure of large complex systems – the orthogonalised linear combination of atomic orbitals (OLCAO) method. Withstanding the test of time, the technique has become one of the most effective for the ab initio calculation of electronic structure and bonding in complex materials, and an important tool for materials science and engineering.

Initially, ESG studies focused on semiconductors and inorganic crystals, alongside non-crystalline solids including amorphous silicon, and inorganic and metallic glass. With time, the team’s interests have extended to materials with more complex structures, including models for grain boundaries in polycrystalline ceramics. In addition, the group expanded its work to explore other material properties – structural, mechanical, magnetic and optical. Alongside the OLCAO method, they began to incorporate cutting-edge computational methods offering different benefi ts and approaches, including the Vienna Ab-initio Simulation Package (VASP).

NEW FORMS OF MATERIAL

Today, focus is retained on the Group’s longstanding areas of interest: complex ceramics and metallic systems. But they are also looking at two new materials classes – laminated ternary intermetallic alloys and biomaterials.

In research funded by the US Department of Energy, Ching and colleagues are studying a

Above. Partial charge distribution on BMV (1js9) protein.Left. Sketches of stacked periodic B-DNA models compensated by Na ions. (a) (AT)10, (b) (GC)10, (c) (AT)5(GC)5 and (d) (AT-GC)5.

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PROFESSOR WAI-YIM CHING

CHALLENGES IN COMPUTATIONAL BIOPHYSICS

OBJECTIVES

To conduct theoretical and computational research for crystalline and non-crystalline materials including biomolecular systems and to develop robust computational methods. Focus is placed on electronic structure, interatomic bonding, charge distribution, mechanical and spectroscopic properties, large-scale simulations and long-range interactions in these materials.

TEAM MEMBERS

For a full list of team members, please visit: http://bit.ly/1vDjwUH

KEY COLLABORATORS

Professor Roger H French; Professor Nicole Steinmetz, Case Western Reserve University, USA • Professor Adrian Parsegian; Professor Rudolf Podgornik, University of Massachusetts-Amherst, USA • Professor Anil Misra, University of Kansas, USA • Professor Paul Rulis; Professor Ridwan Sakidja, University of Missouri-Kansas City (UMKC), USA

FUNDING

US Department of Energy-Basic Energy Sciences (DOE-BES) • DOE-National Energy Technology Laboratory (NETL) • US National Science Foundation • DOE-National Energy Research Scientifi c Computing Center (NERSC) • University of Missouri

CONTACT

Professor Wai-Yim ChingGroup Leader, Electronic Structure Group

Department of Physics and AstronomyUniversity of Missouri-Kansas City 250C Robert H Flarsheim Hall5100 Rockhill Road, Kansas CityMO 64110-2499, USA

T +1 816 235 2503E chingw@umkc.edu

http://bit.ly/YthDvA

PROFESSOR WAI-YIM CHING obtained his BS degree from the University of Hong Kong (1969) and his PhD from Louisiana State University (1974). He joined UMKC in 1978 and was named a University of Missouri System Curators’ Professor in 1988. He is a fellow of the American Physical Society and American Ceramic Society, and has authored or co-authored over 385 journal articles. He and Rulis published a book on the OLCAO method called Electronic Structure Methods for Complex Materials: The orthogonalized linear combination of atomic orbitals (Oxford University Press, 2012).

novel class of laminated ternary intermetallic alloys known as MAX phases; where M is an early transition metal, A is a metalloid element like aluminium and X is carbon or nitrogen. Discovered over 50 years ago, MAX phases have experienced something of a revival in recent years, as Ching underlines: “Because of the unique structural arrangement, MAX phases and their derivatives have outstanding and diverse properties suitable for many applications. They behave both like metals and ceramics, with mechanical properties ranging from ductile to brittle”. Indeed, MAX phase products are already commercially available, with many others under development.

ESG’s second area of focus involves biomaterials, including DNA and peptides. New to the Group, these materials offer great challenges, but also great opportunities. Ching is able to use his own OLCAO method to study these molecules; its use of atomic orbitals for basis expansion in ab initio calculations makes it well suited for the study of large, complex systems like biomolecules. The Group is particularly interested in obtaining new understanding of charge distribution, density of states, charge transfer, bond strength and spectroscopic properties, and is making impressive progress towards achieving this.

ATOMIC-SCALE INFORMATION

Of particular interest to the scientifi c community are the methods ESG has developed to derive atomic-scale information about large proteins. In a study published earlier this year in Polymers, the team demonstrated an amino-acid-based potential method (AAPM), again using OLCAO, on a model of collagen, but also applicable to large proteins.

As a primary structural protein and major component of skin and bone, there has been

intense interest in characterising the structure and function of collagen. While much progress has been made in this regard, there remains a lack of fundamental understanding of its electronic structure at the atomic level.

Using AAPM, Ching was able to calculate the electronic structure and bonding of a model of collagen, obtaining information on density of states, effective charges, bond order values and hydrogen bonding. Furthermore, applying the method to other large proteins, the team has made impressive progress, demonstrating the surface partial charge distribution of the large protein brome mosaic virus (BMV or 1js9), with the calculated surface partial charges on each amino acid in the model retaining at least 95 per cent accuracy. This technique represents a feasible and effi cient way of studying the electronic structure of large complex biomaterials and has garnered signifi cant interest already.

AN EXCITING FUTURE

Through his novel computational models, Ching is revealing an unprecedented level of detail concerning the structure of materials, including proteins. Looking ahead, he plans to continue applying this multidisciplinary approach to different types of materials: “My plan for future research is to focus on new materials and to integrate various computational methods and apply them to even more complex problems”. He is excited about the prospect of future challenges in computational materials research, particularly in biomolecular systems, where there are huge opportunities to learn and contribute. “I don’t believe a single method or theory can solve these problems. The future of computational materials research is exciting, especially for bright and innovative young students with inquiring minds,” he enthusiastically concludes.

Researching recognition

In research published in July, Ching’s team characterised the electronic structureof a cyclic peptide, developing a widely applicable methodology in the process

Molecular recognition is a key principle in biology, critical for cellular signalling and the self-assembly of molecules, cells and even whole organisms. Understanding the mechanistic basis of the interactions between biological macromolecules, at both long and short range, is important for progress in materials science, and could even generate novel functional materials with properties including self-assembly and self-healing.

Making the fi rst steps towards this, ESG and collaborators created a unifi ed methodology for ab initio calculations to reveal the microscopic parameters of such molecular interactions. In turn, these can be input into macroscopic theories of intermolecular bonding. The team applied this methodology to reveal the electronic structure of a peptide, RGD-4C, which recognises cell adhesion molecules called integrins. ESG’s unique methodology will be able to reveal the microscopic parameters of long-range interactions, allowing them to determine the range and strength of interactions between RGD-4C and integrin.

The unifi ed methodology calculations used here, which can generate different microscopic parameters in a single calculation, are the fi rst to enable a reliable estimate of the partial charges and dielectric response for RGD. Furthermore, they have the potential to be applied to other, larger and more complex proteins. They can also be used to refi ne the crucial parameters in molecular dynamics simulations, widely used in biophysics.

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