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The development of advanced materials with high specific energy is crucial for enabling sustainable energy storage solutions, particularly in applications such as lithium-air batteries. Lithium peroxide (Li$_{2}$O$_{2}$) is a key discharge product in non-aqueous lithium-air systems, where its structural and electronic properties significantly influence battery performance. In this work, we investigate the atomic structure, electronic band structure, and Wannier functions of bulk Li$_{2}$O$_{2}$ using density functional theory. The performance of different basis sets of numerical atomic orbitals are compared with respect to a converged plane-wave basis results. We analyze the material's ionic characteristics, the formation of molecular orbitals in oxygen dimers, and the band gap discrepancies between various computational approaches. Furthermore, we develop a localized Wannier basis to model electron-vibration interactions and explore their implications for polaron formation. Our findings provide a chemically intuitive framework for understanding electron-lattice coupling and offer a basis for constructing reduced models that accurately describe the dynamics of polarons in Li$_{2}$O$_{2}$. These insights contribute to the broader goal of improving energy storage technologies and advancing the field of materials design., Comment: 9 pages, 7 figures

First-principles density functional theory (DFT) codes which employ a localized basis offer advantages over those which use plane-wave bases, such as better scaling with system size and better suitability to low-dimensional systems. The trade-off is that care must be taken in order to generate a good localized basis set which is efficient and accurate in a variety of environments. Here we develop and make freely available optimized local basis sets for two common two-dimensional (2D) materials, graphene and hexagonal boron nitride, for the \siesta DFT code. Each basis set is benchmarked against the \abinit plane-wave code, using the same pseudopotentials and exchange-correlation functionals. We find that a significant improvement is obtained by including the $l+2$ polarization orbitals ($4f$) to the basis set, which greatly improves angular flexibility. The optimized basis sets yield much better agreement with plane-wave calculations for key features of the physical system, including total energy, lattice constant and cohesive energy. The optimized basis sets also result in a speedup of the calculations with respect to the non-optimized, native choices.

Spain is the largest producer of avocado and mango fruits in Europe. The majority of production is concentrated in the Axarqu\'ia region in the south, where subtropical fruit plantations and associated water demands have steadily increased over the last two decades. Between 2019-2024, the region underwent an extreme water crisis. Reservoir reserves became nearly depleted and groundwater levels dropped to sea level in several locations, where seawater intrusion is likely, causing large socioeconomic impacts including short-term harvest losses and a long-term loss in economic centrality. We examine the causal pathway that led to this crisis using a mixed-methods approach, combining data from key informant interviews, an exhaustive review of legal documents, and quantitative analysis of time series and spatially explicit data. In particular, we analyze dam water use for irrigation and urban use, meteorological data, reservoir and groundwater levels, and irrigation land cover maps. Our findings show that an unusual meteorological drought was the immediate cause for the decline in reservoir and groundwater reserves (hydrological drought), but the underlying cause was a chronic and structural long-term imbalance between water demand and resources resulting from several structural governance shortcomings: large uncertainties in water resource availability and use hampering effective planning, lack of enforcement of individual water quotas, and the absence of regulatory mechanisms to flexibly impose resource use restrictions at both micro and macro levels based on the overall resources of the system. We propose concrete policy interventions aimed at sustainably enhancing the resilience of the system that can be useful to efficiently manage water shortages in other regions with similar problems.

Loneliness and social isolation among farmers are growing public health concerns. The contributing factors are manifold, and some of them are linked to structural change in agriculture, for instance because of higher workloads, rural depopulation, or reduced opportunities for collaboration. Our work explores the interconnections between loneliness, social contacts, and structural factors in agriculture based on a survey of 110 farm managers in the mountain region of Entlebuch, Switzerland combined with agricultural census data. We use path analysis, in which loneliness is the main outcome, and social contacts are an explanatory and explained variable. We find that 3% of respondents report that they feel lonely frequently or very frequently, and the rest sometimes (20%), rarely (40%) or never (38%). Managers with higher workloads report feeling lonely more frequently, and this relationship is direct, as well as indirect because of less frequent social contacts. However, physical isolation is not a significant predictor of loneliness. Moreover, short food supply chains correlate with less frequent loneliness feelings. Our study sheds light on the effects that structural change can have on the social fabric of rural areas.

Land use expansion is linked to major sustainability concerns including climate change, food security and biodiversity loss. This expansion is largely concentrated in so-called frontiers, defined here as places experiencing marked transformations due to rapid resource exploitation. Understanding the mechanisms shaping these frontiers is crucial for sustainability. Previous work focused mainly on explaining how active frontiers advance, in particular into tropical forests. Comparatively, our understanding of how frontiers emerge in territories considered marginal in terms of agricultural productivity and global market integration remains weak. We synthesize conceptual tools explaining resource and land-use frontiers, including theories of land rent and agglomeration economies, of frontiers as successive waves, spaces of territorialization, friction, and opportunities, anticipation and expectation. We then propose a new theory of frontier emergence, which identifies exogenous pushes, legacies of past waves, and actors anticipations as key mechanisms by which frontiers emerge. Processes of abnormal rent creation and capture and the built-up of agglomeration economies then constitute key mechanisms sustaining active frontiers. Finally, we discuss five implications for the governance of frontiers for sustainability. Our theory focuses on agriculture and deforestation frontiers in the tropics, but can be inspirational for other frontier processes including for extractive resources, such as minerals.

Nanostructured ferroelectrics display exotic multidomain configurations resulting from the electrostatic and elastic boundary conditions they are subject to. While the ferroelectric domains appear frozen in experimental images, atomistic second-principles studies suggest that they may become spontaneously mobile upon heating, with the polar order {\sl melting} in a liquid-like fashion. Here we run molecular dynamics simulations of model systems (PbTiO$_3$/SrTiO$_3$ superlattices) to study the unique features of this transformation. Most notably, we find that the multidomain state looses its translational and orientational orders at different temperatures, resembling the behavior of liquid crystals and yielding an intermediate hexatic-like phase. Our simulations reveal the mechanism responsible for the melting and allow us to characterize the stochastic dynamics in the hexatic-like phase: we find evidence that it is thermally activated, with domain reorientation rates that grow from tens of gigahertzs to terahertzs in a narrow temperature window., Comment: 7 pages, 4 figures

Quantum computing becomes more of a reality as time passes, bringing several cybersecurity challenges. Modern cryptography is based on the computational complexity of specific mathematical problems, but as new quantum-based computers appear, classical methods might not be enough to secure communications. In this paper, we analyse the state of the Galileo Open Service Navigation Message Authentication (OSNMA) to overcome these new threats. This analysis and its assessment have been performed using OSNMA documentation, reviewing the available Post Quantum Cryptography (PQC) algorithms competing in the National Institute of Standards and Technology (NIST) standardization process, and studying the possibility of its implementation in the Galileo service. The main barrier to adopting the PQC approach is the size of both the signature and the key. The analysis shows that OSNMA is not yet prepared to face the quantum threat, and a significant change would be required. This work concludes by assessing different temporal countermeasures that can be implemented to sustain the system's integrity in the short term., Comment: Published in NAVIGATION: Journal of the Institute of Navigation Jun 2024, 71 (2) navi.648; DOI: 10.33012/navi.648 See https://navi.ion.org/content/71/2/navi.6

Complex adaptive systems (CASs), from ecosystems to economies, are open systems and inherently dependent on external conditions. While a system can transition from one state to another based on the magnitude of change in external conditions, the rate of change -- irrespective of magnitude -- may also lead to system state changes due to a phenomenon known as a rate-induced transition (RIT). This study presents a novel framework that captures RITs in CASs through a local model and a network extension where each node contributes to the structural adaptability of others. Our findings reveal how RITs occur at a critical environmental change rate, with lower-degree nodes tipping first due to fewer connections and reduced adaptive capacity. High-degree nodes tip later as their adaptability sources (lower-degree nodes) collapse. This pattern persists across various network structures. Our study calls for an extended perspective when managing CASs, emphasizing the need to focus not only on thresholds of external conditions but also the rate at which those conditions change, particularly in the context of the collapse of surrounding systems that contribute to the focal system's resilience. Our analytical method opens a path to designing management policies that mitigate RIT impacts and enhance resilience in ecological, social, and socioecological systems. These policies could include controlling environmental change rates, fostering system adaptability, implementing adaptive management strategies, and building capacity and knowledge exchange. Our study contributes to the understanding of RIT dynamics and informs effective management strategies for complex adaptive systems in the face of rapid environmental change., Comment: 25 pages, 4 figures, 1 box, supplementary information

We report second-principles simulations on the structural and energetic properties of domains in (PbTiO$_{3}$)$_{n}$/(SrTiO$_{3}$)$_{n}$ superlattices. For the explored layer thickness ($n$ ranging between 8 and 16 unit cells) and lateral sizes of the domains, the most stable configuration corresponds to polar domains separated by a sequence of counter-rotating vortices (clockwise/counterclockwise) perpendicular to the stacking direction and acting as domain walls. The balance between the domain wall energy and the electrostatic energy yields to an optimal domain period $\omega$ that is proportional to the square-root of the thickness of the PbTiO$_{3}$ layer, following the Kittel law. For a given lateral size of the simulation box, suboptimal domain structures (with a width larger than the one predicted by the Kittel law) can be obtained in a metastable form. However, at finite temperature, molecular dynamics simulations show the spontaneous change of periodicity, which implies the formation of new domains whose generation is initiated by the nucleation of vortices and antivortices at the interface between the SrTiO$_{3}$ and the PbTiO$_{3}$ layers. The vortices progressively elongate and eventually annihilate with the antivortices yielding the formation of new domains to comply the Kittel law via a topological phase transition., Comment: 7 pages, 6 Figures

We study the emergence of Berezinskii-Kosterlitz-Thouless (BKT) phases in (PbTiO$_3$)$_3$/(SrTiO$_3$)$_3$ superlattices by means of second-principles simulations. Beyond a threshold tensile epitaxial strain of $\epsilon = 0.25 \%$ the local dipole moments within the superlattices are confined to the film-plane, and thus the polarization can be effectively considered as two-dimensional. The analysis of the decay of the dipole-dipole correlation with the distance, together with the study of the density of defects and its distribution as function of temperature, supports the existence of a BKT phase in a range of temperature mediating the ordered ferroelectric (stable at low $T$), and the disordered paraelectric phase that appears beyond a critical temperature $T_{\rm BKT}$. This BKT phase is characterized by quasi-long-range order (whose signature is a power-law decay of the correlations with the distance), and the emergence of tightly bounded vortex-antivortex pairs whose density is determined by a thermal activation process. The proposed PbTiO$_{3}$/SrTiO$_{3}$ superlattice model and the imposed mechanical boundary conditions are both experimentally feasible, opening the door for the first experimental observation of these new topological phases in ferroelectric materials., Comment: 11 pages, 6 Figures

We study the equilibrium arrangements of polarization vortices in (PbTiO$_3$)$_n$/(SrTiO$_3$)$_n$ superlattices by means of second-principles simulations. We find that, at low temperatures, polarization vortices organize in a regular arrangement in which clockwise and counter-clockwise vortices alternate positions, leading to a crystal-like structure with well defined handedness. This chiral crystal melts at a critical temperature $T_\mathrm{M}$ into a chiral liquid, where long-range order is lost but handedness is preserved. At even higher temperatures, $T_\mathrm{C}$, a second phase transition occurs, at which the chiral liquid of polarization vortices loses its handedness. Both phase transitions can be readily identified by the adequate choices of order parameters., Comment: 7 pages, 4 figures

A theoretical study of cell evolution is presented here. By using a toolbox containing an intracellular catalytic reaction network model and a mutation-selection process, four distinct phases of self-organization were unveiled. First, the nutrients prevail as the central substrate of the chemical reactions. Second, the cell becomes a small-world. Third, a highly connected core component emerges, concurrently with the nutrient carriers becoming the central product of reactions. Finally, the cell reaches a steady configuration where the concentrations of the core chemical species are described by Zipf's law., Comment: 13 pages, 15 figures

Order-disorder transitions are widely explored in various vortex structures in condensed matter physics, i.e., in the type-II superconductors and Bose-Einstein condensates. In this study, we have investigated the ordering of the polar vortex phase in the (PZT)n/(STO)n superlattice systems through phase-field simulations. An antiorder state is discovered for short periodicity superlattice on an SSO substrate, owing to the huge interfacial coupling between PZT and STO as well as the giant in-plane polarization in STO layers due to the large tensile strain. Increasing the periodicity leads to the anti-order to disorder transition, resulting from the loss of interfacial coupling and disappearance of the polarization in STO layers. On the other hand, for short periodicity superlattices, order-disorder-antiorder transition can be engineered by mediating the substrate strain, due to the delicate competition between the depoling effect, interfacial coupling, and strain effect. We envision this study to spur further interest towards the understanding of order-disorder transition in ferroelectric topological structures., Comment: 20 Pages 5 figures

Polar textures have attracted significant attention in recent years as a promising analog to spin-based textures in ferromagnets. Here, using optical second harmonic generation based circular dichroism, we demonstrate deterministic and reversible control of chirality over mesoscale regions in ferroelectric vortices using an applied electric field. The microscopic origins of the chirality, the pathway during the switching, and the mechanism for electric-field control are described theoretically via phase-field modeling and second-principles simulations, and experimentally by examination of the microscopic response of the vortices under an applied field. The emergence of chirality from the combination of non-chiral materials and subsequent control of the handedness with an electric field has far-reaching implications for new electronics based on chirality as a field controllable order parameter., Comment: 19 pages, 4 figures Supplement: 27 pages, 13 figures

Polar skyrmions are predicted to emerge from the interplay of elastic, electrostatic and gradient energies, in contrast to the key role of the anti-symmetric Dzyalozhinskii-Moriya interaction in magnetic skyrmions. With the discovery of topologically-stable polar skyrmions, it is of both fundamental and practical interest to understand the microscopic nature and the possibility of temperature- and strain-driven phase transitions in ensembles of such polar skyrmions. Here, we explore the reversible transition from a skyrmion state (topological charge of -1) to a two-dimensional, tetratic lattice of merons (with topological charge of -1/2) upon varying the temperature and elastic boundary conditions in [(PbTiO3)16/(SrTiO3)16]8 lifted-off membranes. This topological phase transition is accompanied by a change in chirality, from zero-net chirality (in meronic phase) to net-handedness (in skyrmionic phase). To map these changes microscopically required developing new imaging methods. We show how scanning convergent beam electron diffraction provides a robust measure of the local polarization simultaneously with the strain state at sub-nm resolution, while also directly mapping the chirality of each skyrmion. Using this, we demonstrate strain as a crucial order parameter to drive isotropic-to-anisotropic structural transitions of chiral polar skyrmions to non-chiral merons, validated with X-ray reciprocal space mapping and theoretical phase-field simulations. These results revealed by our new measurement methods provide the first illustration of systematic control of rich variety of topological dipole textures by altering the mechanical boundary conditions, which may offer a promising way to control their functionalities in ferroelectric nanodevices using the local and spatial distribution of chirality and order., Comment: 39 pages, 5 figures, 14 supporting figures

Tor and i2p networks are two of the most popular darknets. Both darknets have become an area of illegal activities highlighting the necessity to study and analyze them to identify and report illegal content to Law Enforcement Agencies (LEAs). This paper analyzes the connections between the Tor network and the i2p network. We created the first dataset that combines information from Tor and i2p networks. The dataset contains more than 49k darknet services. The process of building and analyzing the dataset shows that it is not possible to explore one of the networks without considering the other. Both networks work as an ecosystem and there are clear paths between them. Using graph analysis, we also identified the most relevant domains, the prominent types of services in each network, and their relations. Findings are relevant to LEAs and researchers aiming to crawl and investigate i2p and Tor networks.

Orbital angular momentum and torque transfer play central roles in a wide range of magnetic textures and devices including skyrmions and spin-torque electronics(1-4). Analogous topological structures are now also being explored in ferroelectrics, including polarization vortex arrays in ferroelectric/dielectric superlattices(5). Unlike magnetic toroidal order, electric toroidal order does not couple directly to linear external fields. To develop a mechanism that can control switching in polarization vortices, we utilize a high-energy electron beam and show that transverse currents are generated by polar order in the ballistic limit. We find that the presence of an electric toroidal moment in a ferro-rotational phase transfers a measurable torque and orbital angular momentum to the electron beam. Furthermore, we find that the complex polarization patterns, observed in these heterostructures, are microscopically chiral with a non-trivial axial component of the polarization. This chirality opens the door for the coupling of ferroelectric and optical properties.

A review of the present status, recent enhancements, and applicability of the SIESTA program is presented. Since its debut in the mid-nineties, SIESTA's flexibility, efficiency and free distribution has given advanced materials simulation capabilities to many groups worldwide. The core methodological scheme of SIESTA combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, and a real-space grid for the representation of charge density and potentials and the computation of their associated matrix elements. Here we describe the more recent implementations on top of that core scheme, which include: full spin-orbit interaction, non-repeated and multiple-contact ballistic electron transport, DFT+U and hybrid functionals, time-dependent DFT, novel reduced-scaling solvers, density-functional perturbation theory, efficient Van der Waals non-local density functionals, and enhanced molecular-dynamics options. In addition, a substantial effort has been made in enhancing interoperability and interfacing with other codes and utilities, such as Wannier90 and the second-principles modelling it can be used for, an AiiDA plugin for workflow automatization, interface to Lua for steering SIESTA runs, and various postprocessing utilities. SIESTA has also been engaged in the Electronic Structure Library effort from its inception, which has allowed the sharing of various low level libraries, as well as data standards and support for them, in particular the PSML definition and library for transferable pseudopotentials, and the interface to the ELSI library of solvers. Code sharing is made easier by the new open-source licensing model of the program. This review also presents examples of application of the capabilities of the code, as well as a view of on-going and future developments., Comment: 29 pages, 23 figures

We study from first-principles the structural and electronic properties of head-to-head (HH) and tail-to-tail (TT) 180$^\circ$ domain walls in isolated free-standing PbTiO$_{3}$ slabs. For sufficiently thick domains ($n$ = 16 unit cells of PbTiO$_{3}$), a transfer of charge from the free surfaces to the domain walls to form localized electron (in the HH) and hole (in the TT) gases in order to screen the bound polarization charges is observed. The electrostatic driving force behind this electronic reconstruction is clearly visible from the perfect match between the smoothed free charge densities and the bound charge distribution, computed from a finite difference of the polarization profile obtained after the relaxation of the lattice degrees of freedom. The domain wall widths, of around six unit cells, are larger than in the conventional 180$^\circ$ neutral configurations. Since no oxygen vacancies, defects or dopant atoms are introduced in our simulations, all the previous physical quantities are the intrinsic limits of the system. Our results support the existence of an extra source of charge at the domains walls to explain the enhancement of the conductivity observed in some domains walls of prototypical, insulating in bulk, perovskite oxides., Comment: 8 pages, 5 figures

Transition metal dichalcogenide materials $MX_2 (M=Mo,W;X=S,Se)$ are being thoroughly studied due to their novel two-dimensional structure, that is associated with exceptional optical and transport properties. From a computational point of view, Density Functional Theory simulations perform very well in these systems and are an indispensable tool to predict and complement experimental results. However, due to the time and length scales where even the most efficient DFT implementations can reach today, this methodology suffers of stringent limitations to deal with finite temperature simulations or electron-lattice coupling when studying excitation states: the unit cells required to study, for instance, systems with thermal fluctuations or large polarons would require a large computational power. Multi-scale techniques, like the recently proposed Second Principles Density Functional Theory, can go beyond these limitations but require the construction of tight-binding models for the systems under investigation. In this work, we compare two such methods to construct the bands of WSe$_2$. In particular, we compare the result of (i) Wannier-based model construction with (ii) the band fitting method of Liu and co-workers where the top of the valence band and the bottom of the conduction band are modeled by three bands symmetrized to have mainly Tungsten $d_{z^2}$, $d_{xy}$ and $d_{x^2-y^2}$ character. Our results emphasize the differences between these two approaches and how band-fitting model construction leads to an overestimation of the localization of the real-space basis in a tight-binding representation., Comment: 7 pages, 6 figures

We present experiments on detecting hyperpartisanship in news using a 'masking' method that allows us to assess the role of style vs. content for the task at hand. Our results corroborate previous research on this task in that topic related features yield better results than stylistic ones. We additionally show that competitive results can be achieved by simply including higher-length n-grams, which suggests the need to develop more challenging datasets and tasks that address implicit and more subtle forms of bias.

The so-called negative electron compressibility refers to the lowering of the chemical potential of a metallic system when the carrier density increases. This effect has often been invoked in the past to explain the enhancement of the capacitance beyond the classical limits in capacitors with two-dimensional electron gases as electrodes. Based on experiments on strongly confined semiconductor quantum wells (QWs), it has been traditionally ascribed to the electron exchange energy as the main driving force. Recent research, however, has revealed that analogous effects can occur in other classes of materials systems, such as polar oxide interfaces, whose characteristics drastically depart from those of the previously considered cases. To rationalize these new results, it is necessary to revisit the established theory of confined electron gases, and test whether its conclusions are valid beyond the specifics of semiconductor-based QWs. Here we find, based on first-principles calculations of jellium slabs, that one must indeed be very careful when extrapolating existing results to other realistic physical systems. In particular, we identify a number of additional, previously overlooked mechanisms (e.g., related to the displacement of the electronic cloud and to the multiband structure of the delocalized gas), that enter into play and become new sources of negative capacitance in the weak-confinement regime. Our detailed analysis of these emerging contributions, supported by analytic models and multiple test cases, will provide a useful guidance in the ongoing quest for nanometric capacitors with enhanced performance., Comment: 24 pages, 19 figures

The build-factor is a magnitude which allows to correct the photon exponential attenuation model to obtain the real value of a certain dosimetric magnitude, like air exposure. Its main weaknesses are the dependences on the response function of such a magnitude, the geometry, and the source directionality. A formalism to deal with the first is presented in this work, which leads to the definition of the differential build-up factor. Analog Monte Carlo calculations were used to calculate this factor, as well as describing its uncertainty, in the 30 keV to 10 MeV energy range for the most typical materials up to 10 mean-free-paths. Coherent scattering and binding effects were considered in the simulations, which make the results suitable for calculations with the most complete descriptions of the attenuation coefficients. Differences due to geometry, source directionality, and detector response variability were typically found to be up to 30 % in the studied range.

Magnetic skyrmions are mesmerizing spin textures with peculiar topological and dynamical properties, typically the product of competing interactions in ferromagnets, and with great technological potential [1-5]. Researchers have long wondered whether analogous electric skyrmions might exist in ferroelectrics, maybe featuring novel behaviors and possibilities for electric and mechanical control. The results thus far are modest, though: an electric equivalent of the most typical magnetic skyrmion (which would rely on a counterpart of the Dzyaloshinskii-Moriya interaction) seems all but impossible; further, the exotic ferroelectric orders observed or predicted to date [6-8] rely on very specific nano-structures (composites, superlattices), which limits the generality and properties (e.g., mobility) of the possible associated skyrmions. Here we propose an original approach to write electric skyrmions in simple ferroelectric lattices in a customary manner. Our second-principles simulations [9] of columnar ferroelectric nano-domains, in prototype compound PbTiO3 , show that it is possible to harness the Bloch-type internal structure of the domain wall [10] and hence create a genuine skyrmion. We check that the object thus obtained displays the usual skyrmion-defining features; further, it also presents unusual ones, including a symmetry-breaking skyrmion-skyrmion transition driven by strain, various types of topological transformations induced by external fields and temperature, and potentially very small sizes. Our results suggest countless possibilities for creating and manipulating electric textures with non-trivial topologies, using standard experimental tools and materials, effectively inaugurating the field of electric skyrmions., Comment: 5 pages and 3 figures