The Computational 2D Materials Database (C2DB) is a highly curated open database organising a wealth of computed properties for more than 4000 atomically thin two-dimensional (2D) materials. Here we report on new materials and properties that were added to the database since its first release in 2018. The set of new materials comprise several hundred monolayers exfoliated from experimentally known layered bulk materials, (homo)bilayers in various stacking configurations, native point defects in semiconducting monolayers, and chalcogen/halogen Janus monolayers. The new properties include exfoliation energies, Bader charges, spontaneous polarisations, Born charges, infrared polarisabilities, piezoelectric tensors, band topology invariants, exchange couplings, Raman spectra and second harmonic generation spectra. We also describe refinements of the employed material classification schemes, upgrades of the computational methodologies used for property evaluations, as well as significant enhancements of the data documentation and provenance. Finally, we explore the performance of Gaussian process-based regression for efficient prediction of mechanical and electronic materials properties. The combination of open access, detailed documentation, and extremely rich materials property data sets make the C2DB a unique resource that will advance the science of atomically thin materials.

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Discovery of high-performance materials remains one of the most active areas in photovoltaics (PV) research. Indirect band gap materials form the largest part of the semiconductor chemical space, but predicting their suitability for PV applications from first-principles calculations remains challenging. Here, we propose a computationally efficient method to account for phonon-assisted absorption across the indirect band gap and use it to screen 127 experimentally known binary semiconductors for their potential as thin-film PV absorbers. Using screening descriptors for absorption, carrier transport, and nonradiative recombination, we identify 28 potential candidate materials. The list, which contains 20 indirect band gap semiconductors, comprises well-established (3), emerging (16), and previously unexplored (9) absorber materials. Most of the new compounds are anion-rich chalcogenides (TiS3 and Ga2Te5) and phosphides (PdP2, CdP4, MgP4, and BaP3) containing homoelemental bonds and represent a new frontier in PV materials research. Our work highlights the previously underexplored potential of indirect band gap materials for optoelectronic thin-film technologies.

The recent generalised nonlocal optical response (GNOR) theory for plasmonics is analysed, and its main input parameter, namely the complex hydrodynamic convection-diffusion constant, is quantified in terms of enhanced Landau damping due to diffusive surface scattering of electrons at the surface of the metal. GNOR has been successful in describing plasmon damping effects, in addition to the frequency shifts originating from induced-charge screening, through a phenomenological electron diffusion term implemented into the traditional hydrodynamic Drude model of nonlocal plasmonics. Nevertheless, its microscopic derivation and justification is still missing. Here we discuss how the inclusion of a diffusion-like term in standard hydrodynamics can serve as an efficient vehicle to describe Landau damping without resorting to computationally demanding quantum-mechanical calculations, and establish a direct link between this term and the Feibelman d parameter for the centroid of charge. Our approach provides a recipe to connect the phenomenological fundamental GNOR parameter to a frequency-dependent microscopic surface-response function. We therefore tackle one of the principal limitations of the model, and further elucidate its range of validity and limitations, thus facilitating its proper application in the framework of nonclassical plasmonics.

A quantitative and predictive theory of quantum light-matter interactions in ultra thin materials involves several fundamental challenges. Any realistic model must simultaneously account for the ultra-confined plasmonic modes and their quantization in the presence of losses, while describing the electronic states from first principles. Herein we develop such a framework by combining density functional theory (DFT) with macroscopic quantum electrodynamics, which we use to show Purcell enhancements reaching 107 for intersubband transitions in few-layer transition metal dichalcogenides sandwiched between graphene and a perfect conductor. The general validity of our methodology allows us to put several common approximation paradigms to quantitative test, namely the dipole-approximation, the use of 1D quantum well model wave functions, and the Fermi’s Golden rule. The analysis shows that the choice of wave functions is of particular importance. Our work lays the foundation for practical ab initio-based quantum treatments of light-matter interactions in realistic nanostructured materials.

 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

resonances have been realized at visible and infrared wavelengths thanks to the mature lithographic processing of suitable materials, [4] such as silicon (Si), [5] gallium phosphide (GaP), [6] and titanium dioxide (TiO 2 ). [7] It would be desirable to extend the operation of these materials to the ultraviolet, but their small direct band gap energies (≲3 eV) lead to significant absorption losses in the ultraviolet. Wide band gap materials, such as niobium pentoxide [8] and hafnium oxide, [9] offer transparency in the ultraviolet but at the cost of a moderate refractive index (n ≈ 2.1−2.3). Diamond has been theoretically suggested as a potential material, [10,11] but comes with significant nanofabrication challenges. [12] The scarcity of available high-index materials with wide band gap energies calls for the identification of new materials which can advance the rich optical properties of Mie resonances observed in the visible to the ultraviolet. Concurrent advances in first-principles methodology and computing power have recently made it possible to design and discover new materials via high-throughput computations. [13][14][15][16][17] The approach has been successfully applied in several domains, including photovoltaics, transparent conductors, and photocatalysis. [18][19][20] However, to the best of our knowledge, computational discovery of new high-index materials remains largely unexplored. Relevant previous work in this direction has been limited to the static response regime [21,22] reflecting the fact that the major materials databases so far has focused on ground state properties.Here we use high-throughput linear response density functional theory (DFT) to screen an initial set of 2743 elementary and binary materials with the aim to identify isotropic highindex, low loss, and broad band optical materials. For the most promising materials, the computed frequency-dependent complex refractive indices are used as input for Mie scattering calculations to evaluate their optical performance. In addition to the already known high-index materials we identify several new compounds. In particular, boron phosphide (BP) offers a refractive index above three with very low absorption losses in a spectral range spanning from the infrared to the ultraviolet. We then prepare BP nanoparticles and show, by means of darkfield optical measurements and electron energy-loss spectroscopy, that they support size-dependent Mie resonances in the visible and ultraviolet. Finally, we demonstrate a laser reshaping Controlling ultraviolet light at the nanoscale using optical Mie resonances holds great promise for a diverse set of applications, such as lithography, sterilization, and biospectroscopy. Access to the ultraviolet requires materials with a high refractive index and wide band gap energy. Here, the authors systematically search for such materials by computing the frequency-dependent optical permittivity of 338 binary semiconductors and insulators from first principles, and evaluate their scattering properties using Mie theor...

The two-dimensional material hexagonal boron nitride (hBN) hosts luminescent centres with emission energies of ∼ 2 eV which exhibit pronounced phonon sidebands. We investigate the microscopic origin of these luminescent...