NEWS OF THE WEEK COMPUTATIONAL
CHEMISTRY
CALCULATING AT THE INTERFACE Challenging interfacial properties yield to new theoretical methods
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S I N G RECENTLY D E V E L -
oped computational methods, researchers have demonstrated that properties of interfaces can be calculated accurately—giving excellent agreement with experimental results. This means that more complex chemical systems can now be investigated with theoretical tools, hopefully leading to greater understanding of interfacial bonding mechanisms. Thin films of one material on another—for example, metals on metal oxides—are at the heart of numerous applications in microelectronics, sensing, heterogeneous catalysis, and other areas. Ifet despite the technological importance of such unions of materials, scientists do not have a firm handle on bond strengths and adhesion energies at interfaces. For example, quantum mechanical calculations ofadhesion energies based on density functional theory (DFT) give widely varying results, depending on the particular form of computational method employed. But now, Ann E. Mattsson and Dwight R. Jennison, surface scientists at Sandia National Laboratories, have shown that by using corrected mathematical forms of a metal and metal oxide's surface energy—a property that governs wetting and adhesion between dissimilar materials—calculated adhesion energies match experimentally measured values regardless of the particular D F T method used for computation. Specifically, the team found that the energy of adhesion ofpalladium on a-alumina determined from DFT-based "local density" and "generalized gradient" apHTTP://PUBS.ACS.ORG/CEN
proximation methods—if corrected—agree with each other and with experimental data [Surf Set., 520, L611 (2002)}. The work builds on recent advances in computing surface energies made by Mattsson and Chemistry Nobel Laureate and University of California, Santa Barbara, chemistry professor Walter Kohn. In a commentary published in the same issue of Surface Science, Gianfranco Pacchioni, a professor of materials science at the University of Milan, Italy, describes the work as a "new and important contribution." Explaining that bonding at surfaces can change from site to site because of defects, dopants, and variations in CLIMATE
PROMISING Sandia theoreticians Jennison (left) and Mattsson apply computational methods to investigate properties of metal-metal oxide interfaces. electronic and geometric structure, Pacchioni remarks that "it's no wonder that the description of the metal/oxide interface is a challenge for theory" Charles T Campbell, a professor of chemistry at the University of^^hington, Seattle, says, "The theoretical success promises, at last, some understanding of the elusive bonding mechanism at suchinterfaces."-MITCH JACOBY
TALKS
Little Progress Made In New Delhi
D
This final draft, unlike its earlier counterparts, urges countries to ratify the Kyoto protocol— which establishes greenhouse gas reduction targets for 40 developed countries—"in a timely manner." However, the main thrust of the declaration is on adaptation to climate change. The European Union had wanted the declaration to say that developing countries would, in the future, adopt emissions-reduction targets. However, the U.S. allied itself with Saudi Arabia in encouraging developing countries not to make any commitment to reducing greenhouse gases, even though total emissions from China, Mexico, and India are expected to exceed those of industrialized nations withinIO years. The U.S. warned that deep emissions cuts would wreck the economies of developing countries. The final document says only that each develSEEKERS Activists from the India Climate oping country should integrate "policies and measures to protect the climate system with naJustice Forum strive to make their views tional development programs."—BETTE HILEMAN known to climate conference delegates.
elegates failed to make substantial progress on several key issues during the latest round of United Nations climate change negotiations in New Delhi, India. On the final day of the 8th Session of the Conference of Parties to the United Nations Framework on Climate Change, the ministers in attendance adopted a Delhi Declaration on Climate Change & Sustainable Development.
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