We present a direct method for solving the inverse problem of designing isotropic potentials that cause self-assembly into target lattices. Each potential is constructed by matching its energy spectrum to the reciprocal representation of the lattice to guarantee that the desired structure is a ground state. We use the method to self-assemble complex lattices not previously achieved with isotropic potentials, such as a snub square tiling and the kagome lattice. The latter is especially interesting because it provides the crucial geometric frustration in several proposed spin liquids.

Patchy colloids are promising candidates for building blocks in directed self-assembly, but large scale synthesis of colloids with controlled surface patterns remains challenging. One potential fabrication method is to self-assemble the surface patterns themselves, allowing complex morphologies to organize spontaneously. For this approach to be competitive, prediction and control of the pattern formation process are necessary. However, structure formation in many-body systems is fundamentally hard to understand, and new theoretical methods are needed. Here we present a theory for self-assembling pattern formation in multi-component systems on the surfaces of colloidal particles, formulated as an analytic technique that predicts morphologies directly from the interactions in an effective model. As a demonstration we formulate an isotropic model of alkanethiols on gold, a suggested system for directed self-assembly, and predict its morphologies and transitions as a function of the interaction parameters.

We present results from particle simulations with isotropic medium range interactions in two dimensions. At low temperature novel types of aggregated structures appear. We show that these structures can be explained by spontaneous symmetry breaking in analytic solutions to an adaptation of the spherical spin model. We predict the critical particle number where the symmetry breaking occurs and show that the resulting phase diagram agrees well with results from particle simulations.PACS numbers: 89.75. Kd, 75.10.Hk, 05.65.+b Understanding the principles behind spontaneous formation of structured morphologies is of interest both as a fundamental scientific question and in engineering applications where the possibility of using self-assembly to produce novel materials provides a compelling complement to traditional blue-printed fabrication [1,2]. Consequently there is growing interest in exploring interactions that can facilitate self-fabrication of materials with novel properties [3][4][5]. The more general question of what structures are possible to self-assemble from a given class of interactions has however not been addressed, with some notable exceptions e.g. simulation based analysis of polyhedral packing [6].To examine the possibilities of self-assembly from a theoretical angle, in this Letter we consider systems with pair-wise isotropic interactions, frequently used as coarse grained models of more complex meso-scale systems such as colloidal systems [7], particles in an ambient fluid [8,9], and spin glasses [10]. We show that typical aggregates appearing as low temperature configurations in particle simulations with randomly generated medium range isotropic interactions can be predicted analytically using an adaptation of the spherical spin model [11]. The morphologies, many of them novel and surprisingly complex, can be systematically classified by their spontaneous breaking of the rotational symmetry.To formulate a solvable model of a particle system we start by considering a lattice spin system with Hamiltonian on the formwhere s i ∈ {0, 1}, and s i = 1 represents a particle at lattice site i and s i = 0 represents vacuum. The total number of particles is set by the normalization i s i = N . The interaction U ij is an effective isotropic potential with a hard core repulsion corresponding to the lattice spacing. In a spin glass metal the interaction is mediated by a polarization of the Fermi sea [12] while in a colloidal system it could involve a surface polymer induced steric hindrance competing with a depletion attraction [13]. The discrete model described by Eq. (1) can equivalently be formulated as a continuous one (s i ∈ R) with auxiliary constraints, i s m i = N ∀m. To make the model analytically tractable we relax the constraints to include only the first two moments. The result is the spherical spin model including an external field, with Hamiltonian H s = ij U ij s i s j + h i s i . A necessary condition for an energy minimum in this model is j (U ij − λδ ij )s j = h/2, where δ is the identity...

We present a method that systematically simplifies isotropic interactions designed for targeted selfassembly. The uncertainty principle is used to show that an optimal simplification is achieved by a combination of heat kernel smoothing and Gaussian screening of the interaction potential in real and reciprocal space. We use this method to analytically design isotropic interactions for self-assembly of complex lattices and of materials with functional properties. The derived interactions are simple enough to narrow the gap between theory and experimental implementation of theory based designed self-assembling materials.

We show that chiral symmetry can be broken spontaneously in one-component systems with isotropic interactions, i.e., many-particle systems having maximal a priori symmetry. This is achieved by designing isotropic potentials that lead to self-assembly of chiral surfaces. We demonstrate the principle on a simple chiral lattice and on a more complex lattice with chiral supercells. In addition, we show that the complex lattice has interesting melting behavior with multiple morphologically distinct phases that we argue can be qualitatively predicted from the design of the interaction.

Patchy colloidal particles are promising candidates for building blocks in directed self-assembly. To be successful the surface patterns need to be simple enough to be synthesized, while feature-rich enough to cause the colloidal particles to self-assemble into desired structures. Achieving this is a challenge for traditional synthesis methods. Recently it has been suggested that surface patterns themselves can be made to self-assemble. In this paper we present a design path for the hierarchical targeted self-assembly of patchy colloidal particles based on self-assembling surface patterns. At the level of the surface structure, we use a predictive method utilizing the universality of stripes and spots, coupled with stoichiometric constraints, to cause highly specific and functional patterns to self-assemble on spherical surfaces. We use a minimalistic model of an alkanethiol on gold as a demonstration, showing that even with limited control over the interaction between surface constituents we can obtain patterns that cause the colloidal particles themselves to self-assemble into various complex geometric structures, such as strings, membranes, cubic aggregates and colloidosomes, as well as various crystalline patterns.

There is strong scientific evidence for the existence of the significant economic value of several climate-related co-benefits. However, these are seldom recognised in policy-making, and knowledge is still scarce on some co-benefit types and categories. To identify research needs and highlight policy-making opportunities, we propose a new framework and three-type-taxonomy of climate-related co-benefits. We define climate policy co-benefits, such as improved air quality, as ‘Type 1’; co-benefits for climate objectives from policy-making in other fields, such as taxation, as ‘Type 2’; and co-benefits from policies designed to achieve multiple objectives as ‘Type 3’. In order to apply the framework and to analyse how co-benefits have been regarded in policy-making in a climate pioneering country, we also explore the case of Sweden. It is shown that several co-benefits exist, but that these are overlooked almost entirely in policy-making, constituting a bias against climate mitigation. In order to counteract this problem, the article presents a number of recommendations, including a call to researchers to identify and quantify additional co-benefits and to policy-makers on governance reforms, including the need to organise policy-making processes and set decision criteria that promote the consideration of co-benefits.

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