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Nature of the excited states of layered systems and molecular excimers: Exciplex states and their dependence on structure
摘要： Weakly bound systems, like noble-gas dimers or two-dimensional layered materials (graphite, hexagonal boron nitride, or transition-metal dichalcogenides), exhibit excited electronic states of a particular nature. These so-called exciplex states combine on-site (or intralayer) and charge-transfer (or interlayer) configurations in a well-balanced way. We show by ab initio many-body perturbation theory that the energy and composition of the exciplex states depend sensitively on the bond length or interlayer distance of the material. When the constituents approach each other, the charge-transfer contribution increases and the excitation is redshifted to lower energy. If the system is excited into the exciplex state, then a covalent-like bond results. In consequence, noble-gas dimers form excimer complexes, while layered materials exhibit interlayer contraction.
关键词： charge-transfer excitations,many-body perturbation theory,interlayer contraction,exciplex states,layered systems
更新于2025-09-23 15:22:29
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Plasmonic performance of Au <sub/>x</sub> Ag <sub/>y</sub> Cu <sub/>1a??xa??y</sub> alloys from many-body perturbation theory
摘要： We present a detailed appraisal of the optical and plasmonic properties of ordered alloys of the form AuxAgyCu1-x-y, as predicted by means of first-principles many-body perturbation theory augmented by a semi-empirical Drude–Lorentz model. In benchmark simulations on elemental Au, Ag, and Cu, we find that the random-phase approximation (RPA) fails to accurately describe inter-band transitions when it is built upon semi-local approximate Kohn–Sham density-functional theory band-structures. We show that non-local electronic exchange-correlation interactions sufficient to correct this, particularly for the fully-filled, relatively narrow d-bands which contribute strongly throughout the low-energy spectral range (0–6 eV), may be modeled very expediently using band-stretching operators that imitate the effect of a perturbative G0W0 self-energy correction incorporating quasiparticle (QP) mass renormalization. We thereby establish a convenient work-flow for carrying out approximated G0W0 + RPA spectroscopic calculations on alloys and, in particular here, we have considered alloy concentrations down to 12.5% in AuxAgyCu1-x-y, including all possible crystallographic orderings of face-centred cubic type. We develop a pragmatic procedure for calculating the Drude plasmon frequency from first principles, including self-energy effects, as well as a semi-empirical scheme for interpolating the plasmon inverse lifetimes between stoichiometries. A distinctive M-shaped profile is observed in both quantities for binary alloys, in qualitative agreement with previous experimental findings. A range of optical and plasmonic figures of merit are discussed, and plotted for ordered AuxAgyCu1-x-y at three representative solid-state laser wavelengths. On this basis, we predict that certain compositions may offer improved performance over elemental Au for particular application types. We predict that while the loss functions for both bulk and surface plasmons are typically diminished in strength through binary alloying, certain stoichiometric ratios may exhibit higher-quality (longer-lived) localized surface-plasmons and surface-plasmon polaritons, at technologically-relevant wavelengths, than those in elemental Au.
关键词： alloy design for plasmonics,theoretical spectroscopy,many-body perturbation theory
更新于2025-09-23 15:21:01
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Termini effects on the optical properties of graphene nanoribbons
摘要： We investigate from first principles the optical response of finite-length armchair-edged graphene nanoribbons (AGNRs) within the framework of many-body perturbation theory. As a result of the explicit inclusion of zigzag extremities, we identify low-energy and low-intensity excitations that are expected to be almost independent of the GNR length. These excitations coexist with bulk-like excitations, which have the same origin as the ones characterizing infinite AGNRs. Our results are used to rationalize termini effects on the optical response of GNRs and to shed light on recent photoluminescence data.
关键词： graphene nanoribbons,optical properties,photoluminescence,many-body perturbation theory,zigzag extremities
更新于2025-09-10 09:29:36