Nanostructure determination from the pair distribution function: A parametric study of the INVERT approach

We present a detailed study of the mechanism by which the INVERT method [Phys. Rev. Lett. 104, 125501] guides structure refinement of disordered materials. We present a number of different possible implementations of the central algorithm and explore the question of algorithm weighting. Our analysis includes quantification of the relative contributions of variance and fit-to-data terms during structure refinement, which leads us to study the roles of density fluctuations and configurational jamming in the RMC fitting process. We present a parametric study of the pair distribution function solution space for C60, a-Si and a-SiO2, which serves to highlight the difficulties faced in developing a transferable weighting scheme.Comment: 15 pages, 7 figures, formatted for JPCM (RMC issue

Structure determination of disordered materials from diffraction data

We show that the information gained in spectroscopic experiments regarding the number and distribution of atomic environments can be used as a valuable constraint in the refinement of the atomic-scale structures of nanostructured or amorphous materials from pair distribution function (PDF) data. We illustrate the effectiveness of this approach for three paradigmatic disordered systems: molecular C60, a-Si, and a-SiO2 . Much improved atomistic models are attained in each case without any a-priori assumptions regarding coordination number or local geometry. We propose that this approach may form the basis for a generalised methodology for structure "solution" from PDF data applicable to network, nanostructured and molecular systems alike.Comment: 4 pages, 3 figures, set out as for PR

Design of crystal-like aperiodic solids with selective disorder--phonon coupling

Functional materials design normally focuses on structurally-ordered systems because disorder is considered detrimental to many important physical properties. Here we challenge this paradigm by showing that particular types of strongly-correlated disorder can give rise to useful characteristics that are inaccessible to ordered states. A judicious combination of low-symmetry building unit and high-symmetry topological template leads to aperiodic "procrystalline" solids that harbour this type of topological disorder. We identify key classes of procrystalline states together with their characteristic diffraction behaviour, and establish a variety of mappings onto known and target materials. Crucially, the strongly-correlated disorder we consider is associated with specific sets of modulation periodicities distributed throughout the Brillouin zone. Lattice dynamical calculations reveal selective disorder-phonon coupling to lattice vibrations characterised by these same periodicities. The principal effect on the phonon spectrum is to bring about dispersion in energy rather than wave-vector, as in the poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This property of procrystalline solids suggests a mechanism by which strongly-correlated topological disorder might allow new and useful functionalities, including independently-optimised thermal and electronic transport behaviour as required for high-performance thermoelectrics.Comment: 4 figure

Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework

Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the strongest isotropic negative thermal expansion (NTE) effect yet reported for a metal-organic framework (MOF). Incorporation of correlated vacancy defects within the framework affects both the extent of thermal densification and the magnitude of NTE observed in the densified product. We thus demonstrate that defect inclusion can be used to tune systematically the physical behaviour of a MOF.Comment: 8 pages, 4 figures, revise

The 2016 Referendum, Brexit and the Left Behind: An Aggregate-level Analysis of the Result

Why did Britain vote for Brexit? What was the relative importance of factors such as education, age, immigration and ethnic diversity? And to what extent did the pattern of public support for Brexit across the country match the pattern of public support in earlier years for eurosceptic parties, notably the UK Independence Party (UKIP)? In this article we draw on aggregate-level data to conduct an initial exploration of the 2016 referendum vote. First, we find that turnout was generally higher in more pro-Leave areas. Second, we find that public support for Leave closely mapped past support for UKIP. And third, we find that support for Leave was more polarised along education lines than support for UKIP ever was. The implication of this finding is that support for euroscepticism has both widened and narrowed—it is now more widespread across Britain but it is also more socially distinctiv

The 2017 General Election, Brexit and the Return to Two-Party Politics: An Aggregate- Level Analysis of the Result

The outcome of the 2017 general election—a hung parliament—defied most predictions. In this article, we draw on aggregate-level data to conduct an initial exploration of the vote. What was the impact of Brexit on the 2017 general election result? What difference did the collapse of UKIP make? And what was the relative importance of factors such as turnout, education, age and ethnic diversity on support for the two main parties? First, we find that turnout was generally higher in more pro-remain areas, and places with high concentrations of young people, ethnic minorities and university graduates. Second, we find that the Conservatives made gains in the sort of places that had previously backed Brexit and previously voted for UKIP. But, third, we find that the gains the Conservatives made from the electoral decline of UKIP were offset by losses in the sort of places that had previously supported the Conservatives, particularly areas in southern England with larger numbers of graduates. The implication of these findings is that while a Brexit effect contributed to a ‘realignment on the right’, with the Conservative strategy appealing to people in places that had previously voted for UKIP, this strategy was not without an electoral cost, and appears to have hurt the party in more middle class areas