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IBM researchers use supercomputers to help Ford study corrosion

From first principles to industrial applications

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Zurich, Switzerland, 19 Oct 1998—Researchers at Ford and IBM have completed the first realistic simulations of the hydration of aluminum oxide surfaces. This is the first time that first principles (ab initio) computational methods have been used to simulate chemical reactions in technologically relevant surface science.

A product of a collaboration between scientists at Ford Research Laboratory in Dearborn Michigan and IBM Research - Zurich, the research modeled the interaction of water with the surface of alumina (aluminum oxide). Such a surface is important in the adhesive bonding of aluminum alloys, which are increasingly used in light weight automobiles, and these studies will lead to new insights into preventing their corrosion. The research was carried out by Kenneth C. Hass and William F. Schneider of Ford, and Alessandro Curioni and Wanda Andreoni of IBM.

Modeling from first principles

The simulation technique used in this work had been developed in the late 1980's by Roberto Car, now at the University of Geneva, and Michele Parrinello, now at Max Planck Institute in Stuttgart, and formerly of IBM Research - Zurich. The method overcame the drawbacks of earlier approaches to simulating how individual atoms interacted with each other during chemical and physical processes. These older molecular dynamics models used approximate, empirically derived models to describe the forces between the atoms. Unfortunately, in many circumstances the models broke down when large changes occurred, such as when molecules broke apart (dissociated).

In contrast, the Car-Parrinello method uses a highly accurate calculation of the electronic structure of the system as the basis for evaluating the forces between the atoms. This calculation is based on the groundbreaking density-functional theory of Walter Kohn, for which he was the co-recipient of the 1998 Nobel Prize in Chemistry. In this way, the forces are calculated from the principles of quantum mechanics, without using any empirically derived approximations. Thus the computational scheme comes from "first principles", or ab initio, and remains, unlike empirical models, valid in all situations.

Researchers at IBM Research - Zurich have become experts in applying the ab initio method to a variety of problems, including the properties of silicon and the chemistry of fullerenes, the strange carbon molecules that look like the geodesic domes designed by Buckminster Fuller, or the electronic properties of organic light emitting materials. However, up to now, the methods had not been used to study chemical reactions in a realistic system that had direct relevance to industry.

Collaboration between Ford and IBM

The current work arose out of an effort to apply ab initio techniques to problems of interest in industry, and at the same time to transfer to other labs the skills needed to use the new methods. A collaboration between Ford and IBM was initiated in 1995 with the aim of doing joint research using IBM's latest high-end parallel computer, the RS6000-SP. This computer, which links together up to 512 processors to work in parallel, has the speed that makes possible more ambitious and complex ab initio simulations.

"We asked the Ford researchers to propose some topics for joint work, and they suggested that we study alumina surfaces and their interaction with water", explains Wanda Andreoni, Manager, Computational Materials Sciences at IBM Research - Zurich. Alumina is not only interesting to the auto industry because it is important in the adhesive bonding of aluminum alloys, it's also applied as a support for catalysts in emission control. The reaction with water is important for several reasons, including that it is significant in the chemical reactions that lead to corrosion.

But it was difficult to study the reaction experimentally, in part because it was hard to know what reactions were caused by defects in the alumina surface and which by the substance itself, even in a perfect crystal form. The reactions, taking place in less than a trillionth of a second, are also too rapid for feasible experimental techniques.

Getting results with ab initio models

In a six-month-long effort, the IBM scientists showed Ford researchers how to run simulations using the ab initio molecular dynamics technique. The actual simulations were done by Hass and Schneider at Ford, with close collaboration from Curioni and Andreoni. These were the most complex simulations yet attempted with the Car-Parrinello method, since to get realistic results, 135 aluminum and oxygen atoms, as well as up to 10 water molecules, with a total of about 1000 electrons had to be modeled. The simulation modeled how the molecules behave over a trillionth of a second in time, breaking that time up into ten thousand time-steps. Each simulation run took about a week on the RS6000-SP computer with 32 nodes, operated by Tim Dinger at IBM's T.J. Watson Research Center in Yorktown Heights, NY.

The results have more than justified the effort. One of the key questions had been whether water molecules dissociate - break apart - as they bond to the alumina surface. The simulation showed clearly that they do, very readily. In addition the rates of various reactions, such as dissociation, adsorption onto the surface, and formation of new compounds with the alumina could be easily measured from the simulations. Perhaps most surprisingly, the simulations demonstrated that the reactions changed, and how they changed, as the surface became more and more covered with water molecules. This means that there are important differences between the way the surface acts when actually wetted by liquid water as compared with how it acts when merely moistened by atmospheric humidity. "We also showed that, even on a perfect surface with no defects, reaction rates are very high", Andreoni points out - a result that would have been almost impossible to obtain experimentally because of the difficulty in producing such perfect surfaces.

The research is a first step toward understanding the complex surface processes involving water and aluminum oxide. But equally important, it demonstrates the feasibility of ab initio simulation techniques in studying the dynamics of chemical reactions in complex, realistic systems.

The scientific report on this work was published in Science (Vol. 282, No. 5387, 9 October 1998). The authors of the report "The Chemistry of Water on Alumina Surfaces: Reaction Dynamics from First Principles" are Kenneth C. Hass and William F. Schneider of Ford Research Laboratory in Dearborn MI, USA, and Alessandro Curioni and Wanda Andreoni of IBM Research - Zurich in Rüschlikon.

Press contact

Nicole Strachowski
Media Relations
IBM Research - Zurich
Tel +41 44 724 84 45

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