We describe a remarkably simple, generic, coarse-grained model involving anisotropic interactions, and characterize the global minima for clusters as a function of various parameters. Appropriate choices for the anisotropic interactions can reproduce a wide variety of complex morphologies as global minima, including spheroidal shells, tubular, helical and even head-tail morphologies, elucidating the physical principles that drive the assembly of these mesoscopic structures. Our model captures several experimental observations, such as the existence of competing morphologies, capsid polymorphism, and the effect of scaffolding proteins on capsid assembly.

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We explore the potential energy landscape for clusters composed of disklike ellipsoidal particles interacting via an anisotropic potential based on the elliptic contact function. Over a wide range of parameter space we find global potential energy minima consisting of helices composed of one or more strands. Characterizing the potential energy surface in the region of helical global minima reveals a topology associated with "structure-seeking" systems. This result indicates that the helices will self-assemble over a wide range of temperature.

Nature has mastered the art of creating complex structures through self-assembly of simpler building blocks. Adapting such a bottom-up view provides a potential route to the fabrication of novel materials. However, this approach suffers from the lack of a sufficiently detailed understanding of the noncovalent forces that hold the self-assembled structures together. Here we demonstrate that nature can indeed guide us, as we explore routes to helicity with achiral building blocks driven by the interplay between two competing length scales for the interactions, as in DNA. By characterizing global minima for clusters, we illustrate several realizations of helical architecture, the simplest one involving ellipsoids of revolution as building blocks. In particular, we show that axially symmetric soft discoids can self-assemble into helical columnar arrangements. Understanding the molecular origin of such spatial organisation has important implications for the rational design of materials with useful optoelectronic applications.anisotropic interactions ͉ columnar arrangements ͉ helix ͉ self-assembly N ature provides ubiquitous examples of helical architecture with diverse functions. Helical structures are common structural motifs in biomolecules and are involved in the storage of genetic information (1). They are also important in solid-and liquid-crystal engineering for fabricating functional materials with useful optoelectronic applications (2-5). For example, discotic molecules in crystalline or liquid crystalline states often exhibit helical order in columnar arrangements (2-6), and such materials are attractive for use in optoelectronic devices because of the exceptional 1D charge-carrier mobilities along the columns (2-4). A common route to induce helicity in columnar arrangements is inclusion of chiral centers in discotic molecules (7). Helical columnar arrangements have also been realized in a few cases with achiral discotic molecules (8, 9), although no general strategy seems to have emerged.Self-assembly is nature's prescription for the creation of complex structures from simpler building blocks (10, 11). Although many novel building blocks have been discovered for self-assembly, differing in shape, composition, and functionality (12, 13), the basic rules that govern this process are not yet understood in sufficient detail to realize target structures routinely through a priori design of building blocks. Here we ask the specific question: Can we learn from nature how to design building blocks that self-assemble into helical structures? In seeking a guiding principle from nature for obtaining helical architectures, we considered DNA, in which two competing length scales exist, one characterizing the distance between consecutive nucleotides in the sugar-phosphate backbone and the other governing the stacking of the base pairs (1). The present contribution thus explores realizations of helical architectures with achiral building blocks driven by the interplay between two competing length scales. To this end, we c...

The AMBER and CHARMM force fields are analyzed from the viewpoint of the permutational symmetry of the potential for feasible exchanges of identical atoms and chemical groups in amino and nucleic acids. In each case, we propose schemes for symmetrizing the potentials, which greatly facilitate the bookkeeping associated with constructing kinetic transition networks via geometry optimization.