Advanced Materials Progress Report on Challenges in Computational Materials Science** By Dierk Raabe* 1. A Model is a Model is a Model Youshouldnotalwaystrustyoursimulation.Why?Because amenaceofconfusingmodelswithrealityalwaysexists.Does anyone nowadays refer to ªfirst principles simulationsº? This point is well taken. However, practically all of the current predictions in this domain are based on simulating electron dynamics using local density functional theory. These simula- tions, though providing a deep insight into materials ground states, are not exact but approximate solutions of the Schrö- dinger equation, whichÐwe should not forgetÐis a model it- self. [1] Doesanyonestillrefertoªfinite-elementsimulationsº? This point is also well taken. However, also in this case one has to admit that approximate solutions to large sets of non- linear differential equations formulated for a (non-existing) continuumunderidealizedboundaryconditionsiswhatitis:a model ofnaturebutnotreality. But let us calm down and render the discussion a bit more seriousness: current methods of ground-state calculations are definitelyamongthecutting-edgedisciplinesincomputational materialsscienceandthecommunityhaslearntmuchfromit during the last years. Similar aspects apply for some contin- uum-based finite-element simulations. After all, this article is meant to attract readers into this exciting field and not to repulsethem.AndforthisreasonIfeelobligedtofirstmake a point in underscoring that any interpretation of a research result obtained by computer simulation should be accompa- niedbyscrutinizingthemodelingredientsandboundarycon- ditions of that calculation in the same critical way as an experimentalistwouldcheckhisexperimentalset-up. In the following I will address some important aspects of computational materials science. The selection is of course biased (more structural than functional; more metals than non-metals; more mesoscale than atomic scale). I will try to reachabalancebetweenfundamentalandappliedtopics.The article focuses particularly on topics and publications of 2001 and2002. 2. Some Semantics of Modeling and Simulation Before continuing in medias res, let us revisit some basic thoughts on the semantics of modeling and simulation. The words modeling and simulation are often distinguished by somewhat arbitrary arguments or they are simply used syn- onymously. This lack of clarity reflects that concepts in com- putationalmaterialssciencedevelopfasterthansemantics.To establish a common language in this field, a less ambiguous definitionofbothconceptsmightbehelpful.Incurrentunder- standingthewordmodeling(model(Latin,Italian):copy,rep- lica, exemplar) often covers two quite different meanings, namely, model formulation and numerical modeling. The lat- tertermisfrequentlyusedasasynonymfornumericalsimula- tion(simulare(Latin):fake,duplicate,mimic,imitate).Ithink that the general synonymous use of the terms modeling and simulation is not an ideal choice. Rosenblueth and Wiener [2] offered an elegant comment on this point, which underlines thatthecreationofmodelsencompassesamuchmoregeneral conceptthansimulation.Accordingtotheirworkthegeneral intention of a scientific inquiry is to obtain an understanding and a control of some parts of the universe. However, most Adv.Mater. 2002, 14,No.9,May3 Ó WILEY-VCHVerlagGmbH,D-69469Weinheim,2002 0935-9648/02/0905-0639$17.50+.50/0 639 PROGRESS REPORT Progress reports are a new type of article in Advanced Materials, dealing with the hottest current topics, and pro- viding readers with a critically selected overview of important progress in these fields. It is not intended that the articles be comprehensive, but rather insightful, selective, critical, opinionated, and even visionary. We have approached scientists we believe are at the very forefront of these fields to contribute the articles, which will appear on an annual basis. The article below describes the latest advances in computational materials science. ± [*] Prof. D. Raabe Max-Planck-InstitutfürEisenforschung Max-Planck-Str.1,D-40237Düsseldorf(Germany) E-mail:raabe@mpie.de [**] Alsopublishedin Advanced Engineering Materials underthetitle:ªDon't Trust Your SimulationÐComputational Materials Science on Its Way to Maturity?º, Adv. Eng. Mater. 2002, 4,255.