124 research outputs found
Towards an Inclusive and Representative Academic Landscape
No full textThis article is a summary of a panel discussion entitled 'Towards an inclusive and representative academic landscape', held at the Building Bridges Meeting of Academia Europaea and the Young Academy of Europe on 26 October 2022. The panellists were Professor Yvonne Galligan, director of Equality, Diversity and Inclusion and Professor of Comparative Politics at the Technological University Dublin, Dr Katalin Solymosi, plant biologist, assistant professor at Eötvös Loránd University and vice-chair of the Young Academy of Europe, and Professor Stephen Curry, Assistant Provost for Equality, Diversity and Inclusion and Professor of Structural Biology at Imperial College London. Dr Linn Leppert, Associate Professor of Computational Chemical Physics and board member of the Young Academy of Europe chaired the discussion.</p
Assessment of the ab initio Bethe−Salpeter equation approach for the low-lying excitation energies of bacteriochlorophylls and chlorophylls
No full textBacteriochlorophyll and chlorophyll molecules are crucial building blocks of the photosynthetic apparatus in bacteria, algae, and plants. Embedded in transmembrane protein complexes, they are responsible for the primary processes of photosynthesis: excitation energy and charge transfer. Here, we use ab initio many-body perturbation theory within the GW approximation and Bethe−Salpeter equation (BSE) approach to calculate the electronic structure and optical excitations of bacteriochlorophylls a, b, c, d, and e and chlorophylls a and b. We systematically study the effects of the structure, basis set size, partial self-consistency in GW, and the underlying exchange−correlation approximation and compare our calculations with results from time-dependent density functional theory, multireference RASPT2, and experimental literature results. We find that optical excitations calculated with GW+BSE are in excellent agreement with experimental data, with an average deviation of less than 100 meV for the first three bright excitations of the entire family of (bacterio)chlorophylls. Contrary to state-of-the-art time-dependent density functional theory (TDDFT) with an optimally tuned range-separated hybrid functional, this accuracy is achieved in a parameter-free approach. Moreover, GW+BSE predicts the energy differences between the low-energy excitations correctly and eliminates spurious charge transfer states that TDDFT with (semi)local approximations is known to produce. Our study provides accurate reference results and highlights the potential of the GW+BSE approach for the simulation of larger pigment complexes
Optoelectronic Properties of Halide Perovskites with ab Initio Many-body Perturbation Theory
No full textStructural and electronic properties of transition metal nanoalloys and magnetic compounds
No full textDouble trouble: exploring the chemical landscape of halide double perovskites
No full textHalide Double Perovskites (HDPs) are an emerging class of materials with chemical formula A2BB’X6 with possible applications in photovoltaics, X-ray detection, sensing, photocatalysis and spintronics.. However, with more than 40,000 potential HDP compositions, much of the chemical landscape remains unexplored. We have generated a database of spin-polarized, hybrid functional (HSE06) electronic structure data of all HPDs with A=Cs that are predicted to be stable based on a tolerance-factor analysis. Our high-throughput workflow also consists or a chemical bonding and orbital projection analysis based on LOBSTER (ww.cohp.de), leading to a comprehensivedatabase of electronic, magnetic and chemical bonding properties of >2700 HDP compositions, which can serve as a starting point for material design and discovery via interpretable machine learning techniques, which we use to identify unexpected trends and relations in the chemical landscape
Leppert, Chas. W. (Death, 1882-05-06)
No full textAddress: 5th & Front St.Age at death: 25 yrsPg 95/1882/196/M W S/U. S./Dr. Rendigs/Linn/WesleyanOriginal record filed in drawer labeled 'Leonhard-Lewis, P'
Halide perovskites from first principles: From fundamental optoelectronic properties to the impact of structural and chemical heterogeneity
No full textOrganic-inorganic metal-halide perovskite semiconductors have outstanding and widely tunable optoelectronic properties suited for a broad variety of applications. First-principles numerical modelling techniques are playing a key role in unravelling structure-property relationships of this structurally and chemically diverse family of materials, and for predicting new materials and properties. Herein we review first-principles calculations of the photophysics of halide perovskites with a focus on the band structures, optical absorption spectra and excitons, and the effects of electron- and exciton-phonon coupling and temperature on these properties. We focus on first-principles approaches based on density functional theory and Green's function-based many-body perturbation theory and provide an overview of these approaches. While a large proportion of first-principles studies have been focusing on the prototypical ABX3 single perovskites based on Pb and Sn, recent years have witnessed significant efforts to further functionalize halide perovskites, broadening this family of materials to include double perovskites, quasi-low-dimensional structures, and other organic-inorganic materials, interfaces and heterostructures. While this enormous chemical space of perovskite and perovskite-like materials has only begun to be tapped experimentally, recent advances in theoretical and computational methods, as well as in computing infrastructure, have led to the possibility of understanding the photophysics of ever more complex systems. We illustrate this progress in our review by summarizing representative studies of first-principles calculations of halide perovskites with various degrees of complexity
First principles atomistic theory of halide perovskites
No full textNumerical modeling methods that do not rely on empirical input but only on the first principles of physics can provide atomistic understanding, validate experimental observations, and predict emerging properties and new materials. Halide perovskites have equally challenged and inspired researchers that develop and use such methods. Their soft and highly anharmonic lattices, featuring rotating molecules and migrating ions, intricate coupling between structural and electronic degrees of freedom, and complex electronic and excited state structures, call for computer experiments at the verge of (and often beyond) technical feasibility. This has led to the development of new models, new approaches, and a general push for expanding the applicability of state-of-the-art first-principles techniques. This chapter aims to assist newcomers to the field in understanding the basic theory of common first-principles methods, with a focus on the challenges associated with practical calculations of structural and optoelectronic properties of halide perovskites.</p
The Electronic Structure of Gold−Platinum Nanoparticles: Collecting Clues for Why They Are Special
No full textExcitons in metal-halide perovskites from first-principles many-body perturbation theory
No full textMetal-halide perovskites are a structurally, chemically, and electronically diverse class of semiconductors with applications ranging from photovoltaics to radiation detectors and sensors. Understanding neutral electron–hole excitations (excitons) is key for predicting and improving the efficiency of energy-conversion processes in these materials. First-principles calculations have played an important role in this context, allowing for a detailed insight into the formation of excitons in many different types of perovskites. Such calculations have demonstrated that excitons in some perovskites significantly deviate from canonical models due to the chemical and structural heterogeneity of these materials. In this Perspective, I provide an overview of calculations of excitons in metal-halide perovskites using Green’s function-based many-body perturbation theory in the GW + Bethe–Salpeter equation approach, the prevalent method for calculating excitons in extended solids. This approach readily considers anisotropic electronic structures and dielectric screening present in many perovskites and important effects, such as spin–orbit coupling. I will show that despite this progress, the complex and diverse electronic structure of these materials and its intricate coupling to pronounced and anharmonic structural dynamics pose challenges that are currently not fully addressed within the GW + Bethe–Salpeter equation approach. I hope that this Perspective serves as an inspiration for further exploring the rich landscape of excitons in metal-halide perovskites and other complex semiconductors and for method development addressing unresolved challenges in the field
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