The interface of quantum mechanics methods with classical atomistic simulation techniques, such as molecular dynamics and Monte Carlo, continues to be an area of considerable promise and interest. Such coupled quantum–atomistic approaches have been developed and employed, for example, to gain a comprehensive understanding of the energetics, kinetics, and dynamics of chemical processes involving surfaces and interfaces of hard materials. More recently, it has become possible to directly couple first-principles electronic structure techniques to continuum solid mechanics, either on the fly with feedback between length scales or by information passing between length scales. We discuss, with tutorial examples, the merging of quantum mechanics with molecular dynamics and Monte Carlo simulations, as well as quantum–continuum coupled techniques. We illustrate the opportunities offered by incorporation of information from quantum mechanics (reducing assumptions in higher length-scale models) and outline the challenges associated with achieving full predictive capability for the behavior of materials.

Many aspects of materials deformation and failure are controlled by atomic-scale phenomena that can be explored using molecular statics and molecular dynamics simulations. However, many of these phenomena involve processes on multiple length scales with the result that full molecular statics/molecular dynamics simulations of the entire system are too large to be tractable. In this review, we discuss hybrid models that perform molecular statics/molecular dynamics simulations “without all the atoms,” aimed at retaining atomistic detail at a fraction of the computational cost. These methods couple a fully atomistic model in critical regions to regions described by less-expensive continuum methods where they can provide an adequate representation of the important physics. We give an overview of the challenges such models present, with a focus on recent work to address issues of dynamics and finite (non-zero) temperature.

Coarse-grained modeling is a key component in the field of multiscale simulation. Many biomolecular and otherwise complex systems require the characterization of phenomena over multiple length and time scales in order to fully resolve and understand their behavior. These different scales range from atomic to near macroscopic dimensions, and they are generally not independent of one another, but instead coupled. That is, phenomena occurring at atomic length scales have an effect at macroscopic dimensions and vice versa. Systematic transfer of information between these different scales represents a core challenge in the field of multiscale simulation. Coarse-grained modeling works at an intermediate resolution that can bridge the very high resolution (atomic) scale to the very low resolution (macroscopic) scale. As such, a significant challenge is the development of a systematic methodology whereby coarse-grained models can be derived from their high-resolution atomistic-scale counterpart. Here, a systematic theoretical and computational methodology will be described for developing coarse-grained representations of biomolecular and other soft-matter systems. At the heart of the methodology is a variational statistical mechanical algorithm that uses forcematching of atomistic molecular dynamics data to a coarse-grained representation. A theoretical analysis of the coarse-graining methodology will be presented, along with illustrative applications to membranes, peptides, and carbohydrates.

With the guidance offered by nonequilibrium statistical thermodynamics, simulation techniques are elevated from brute-force computer experiments to systematic tools for extracting complete, redundancy-free, and consistent coarse-grained information for dynamic systems. We sketch the role and potential of Monte Carlo, molecular dynamics, and Brownian dynamics simulations in the thermodynamic approach to coarse graining. A melt of entangled linear polyethylene molecules serves us as an illustrative example.

Disordered, glassy materials are arguably one of the least understood states of condensed matter. Yet, they are ubiquitous in everyday life (polymers, “soft” glasses such as toothpaste, various emulsions, pastes, and foams) and in demanding applications (metallic glasses). Much of what is known about this important class of materials has been the result of truly concerted experimental and molecular modeling efforts. It is now generally accepted that amorphous materials exhibit dynamic and mechanical heterogeneities, but efforts to incorporate these into truly multiscale modeling approaches have been limited. This article describes the current state of affairs, along with many of the challenges that must be met to arrive at a fundamental understanding of amorphous materials and their response to external stresses.

The following article is based on the Von Hippel Award address given by Knut W. Urban, chair of experimental physics at RWTH Aachen University and director of the Institute of Microstructure Research within the Department of Solid-State Research at the Jülich Research Center. Urban presented his award talk on November 29, 2006, during the 2006 Materials Research Society Fall Meeting in Boston. He was recognized with MRS's highest honor, the Von Hippel Award, for his “sustained contributions to the development and use of electron microscopy, and for major discoveries in the defect physics of quasicrystals and high-temperature superconductors.” The Von Hippel Award honors those qualities most prized by materials scientists and engineers—brilliance and originality of intellect, combined with vision that transcends the boundaries of conventional scientific disciplines, as exemplified by the life of Arthur von Hippel (http://vonhippel.mrs.org).

In this article, Urban describes the advances in spherical-aberration-corrected electron optics that have set transmission electron microscopy on an entirely new track in materials science. The new imaging theory for aberration-corrected instruments is based on exploiting both lens focus and spherical aberration as variable parameters to optimize contrast, resolution, and point spread. The novel negative-spherical-aberration imaging technique makes it possible to image low-nuclear-charge atoms, which were previously inaccessible directly by electron microscopy. This technique has proven particularly successful for research on oxides. Due to negligible point spread, quantitative measurements of atomic-site occupancies, which are equivalent to local concentrations, have become feasible. These improvements are dramatically expanding the potential of electron microscopy for quantitative studies in materials science.