E ngineering mechanics provides excel- lent theoretical descriptions for the ra- tional design of materials and accurate lifetime prediction of mechanical struc- tures. This approach deals with continuous quan- tities such as strain field that are functions of both space and time. Constitutive relations such as Hooke’s law for deformation and Coulomb’s law for friction describe the relationships between these macroscopic fields. These constitutive equations contain material-specific parameters such as elastic moduli and friction coefficients, which are often size dependent. For example, the mechanical strength of materials is inversely pro- portional to the square root of the grain size, ac- cording to the Hall-Petch relationship. Such scaling laws are usually validated experi- mentally at length scales above a micron, but in- terest is growing in extending constitutive rela- tions and scaling laws down to a few nanometers. This is because many experts believe that by re- ducing the structural scale (such as grain sizes) to the nanometer range, we can extend material properties such as strength and toughness be- yond the current engineering-materials limit. 1 In addition, widespread use of nanoelectro- mechanical systems (NEMS) is making their durability a critical issue, to which scaling down engineering-mechanics concepts is essential. Because of the large surface-to-volume ratios in these nanoscale systems, new engineering- mechanics concepts reflecting the enhanced role of interfacial processes might even be necessary. Atomistic simulations will likely play an im- portant role in scaling down engineering- mechanics concepts to nanometer scales. Recent advances in computational methodologies and massively parallel computers have let re- searchers carry out 10- to 100-million-atom atomistic simulations (the typical linear dimen- 56 COMPUTING IN SCIENCE & ENGINEERING MULTISCALE S IMULATION OF NANOSYSTEMS The authors describe simulation approaches that seamlessly combine continuum mechanics with atomistic simulations and quantum mechanics. They also discuss computational and visualization issues associated with these simulations on massively parallel computers. N ANOTECHNOLOGY AIICHIRO NAKANO, MARTINA E. BACHLECHNER, RAJIV K. KALIA, ELEFTERIOS LIDORIKIS, PRIYA VASHISHTA, AND GEORGE Z. VOYIADJIS Louisiana State University TIMOTHY J. CAMPBELL Logicon Inc. and Naval Oceanographic Office Major Shared Resource Center SHUJI OGATA Yamaguchi University FUYUKI SHIMOJO Hiroshima University 1521-9615/01/$10.00 © 2001 IEEE Authorized licensed use limited to: UNIVERSITY OF OSLO. Downloaded on January 14, 2009 at 04:59 from IEEE Xplore. Restrictions apply.