We present a first-principles description of anisotropic materials characterized by having both weak (dispersionlike) and strong covalent bonds, based on the adiabatic-connection fluctuation-dissipation theorem with density functional theory. For hexagonal boron nitride the in-plane and out-of-plane bonding as well as vibrational dynamics are well described both at equilibrium and when the layers are pulled apart. Bonding in covalent and ionic solids is also described. The formalism allows us to ping down the deficiencies of common exchange-correlation functionals and provides insight toward the inclusion of dispersion interactions into the correlation functional. DOI: 10.1103/PhysRevLett.96.136404 PACS numbers: 71.15.Mb, 63.20.ÿe, 71.10.ÿw, 71.15.Nc Soft matter, biomolecules, and layered materials are examples of weakly bonded compounds, which constitute stringent tests for ab initio electronic structure calculations. A successful description of such systems requires an accurate treatment of a whole range of interactions, from short-range covalent to long-range van der Waals (vdW) forces. Moreover, their study provides valuable hints about how to devise new approximations that describe at a reasonable computational cost very different bonding regimes. In this realm, layered materials represent a unique case. The Kohn-Sham (KS) method under the simple local density approximation (LDA) [1] is known to give reasonable structural properties near the equilibrium interlayer distance of systems like graphite [2] and hexagonal boron nitride (h-BN) [3,4]. Surprisingly, the more elaborate exchange-correlation (XC) energy functional based on the generalized-gradient approximation (GGA) [5], while providing a good in-plane bonding, fails dramatically in the description of the equilibrium interlayer distance in h-BN and graphite, leading to completely unphysical results [6,7]. The mechanism responsible for this poor performance is not specific to GGA but to all functionals based on exact exchange [8] plus some LDA correlation (EXXc) (as illustrated below).It has been hypothesized that this failure is due to the lack of description of vdW forces, which are the manifestation of long-range correlation effects [7]. However, LDA, without accounting for vdW interactions, does bind the h-BN and graphite layers. More importantly, recently proposed approximate nonlocal prescriptions beyond LDA or GGA in the vdW density functional (vdW-DF) framework [9], while describing vdW forces, result in a large overestimation of the equilibrium layer-layer distance [7]. Thus, available XC functionals cannot describe correctly a layered material at different geometrical configurations. Consequently, there is a basic need to understand this severe breakdown and how to define a stable, successful scheme to calculate such structural properties. This is the goal of the present Letter. We demonstrate that a fully microscopic, parameter-free approach based on the adiabaticconnection fluctuation-dissipation theorem (ACFDT) [10] correctly describes ...

Semi-classical non-local optics based on the hydrodynamic description of conduction electrons might be an adequate tool to study complex phenomena in the emerging field of nanoplasmonics. With the aim of confirming this idea, we obtain the local and non-local optical absorption spectra in a model nanoplasmonic device in which there are spatial gaps between the components at nanometric and sub-nanometric scales. After a comparison against time-dependent density functional calculations, we conclude that hydrodynamic non-local optics provides absorption spectra exhibiting qualitative agreement but not quantitative accuracy. This lack of accuracy, which is manifest even in the limit where induced electric currents are not established between the constituents of the device, is mainly due to the poor description of induced electron densities.

We present an ab initio study of the hybridization of localized surface plasmons in a metal nanoparticle dimer. The atomic structure, which is often neglected in theoretical studies of quantum nanoplasmonics, has a strong impact on the optical absorption properties when subnanometric gaps between the nanoparticles are considered. We demonstrate that this influences the hybridization of optical resonances of the dimer, and leads to significantly smaller electric field enhancements as compared to the standard jellium model. In addition, we show that the corrugation of the metal surface at a microscopic scale becomes as important as other well-known quantum corrections to the plasmonic response, implying that the atomic structure has to be taken into account to obtain quantitative predictions for realistic nanoplasmonic devices. There is a growing interest in the development and implementation of nanoplasmonic devices such as nanosensors [1,2], nanophotonic lasers [3][4][5], optoelectronic [6,7] and light-harvesting [8,9] structures, and nanoantennas [10,11]. Therefore, it is essential to have theoretical techniques with a sufficient predictive value to understand the physical processes of light-matter interactions at the nanoscale. In this regime, the standard analysis of the plasmonic response to external electromagnetic (EM) fields using the classical macroscopic Maxwell equations must be undertaken with caution. Indeed, genuine quantum effects such as the nonlocal nature of the electron-density response, the inhomogeneity of the conduction-electron density, or the possibility of charge transfer by tunneling have to be considered [12]. These effects can be incorporated into Maxwell equations in an approximate manner using, e.g., nonlocal dielectric functions [13][14][15][16][17][18][19] or the ad hoc inclusion of "virtual" dielectric materials [20][21][22]. While these semiclassical approximations have been successfully applied in many cases, they do not achieve the precision provided by first-principle calculations.A number of recent publications [20,[23][24][25][26][27] have treated the electronic response of plasmonic structures using stateof-the-art time-dependent density functional theory (TDDFT) [28,29]. However, the ionic structure is typically neglected and replaced by a homogeneous jellium background or by an unstructured effective potential. Although this approximation is sometimes justified by the collective nature of plasmon excitations [30,31], the charge oscillations associated with a localized surface plasmon (LSP) are mainly concentrated on the metal-vacuum interface. One may thus expect that the ionic structure in this region will have a quantitative and even qualitative impact. Therefore, there is a need to address the influence of the atomic configuration in the plasmonic response at the nanoscale. In this Rapid Communication we present ab initio calculations including the atomic structure, in accordance with the current paradigm in computational condensed matter physics [32] and physical chem...

Light-matter interaction in plasmonic nanostructures is often treated within the realm of classical optics. However, recent experimental findings show the need to go beyond the classical models to explain and predict the plasmonic response at the nanoscale. A prototypical system is a nanoparticle dimer, extensively studied using both classical and quantum prescriptions. However, only very recently, fully ab initio time-dependent density functional theory (TDDFT) calculations of the optical response of these dimers have been carried out. Here, we review the recent work on the impact of the atomic structure on the optical properties of such systems. We show that TDDFT can be an invaluable tool to simulate the time evolution of plasmonic modes, providing fundamental understanding into the underlying microscopical mechanisms

The performance of many-body perturbation theory for calculating groundstate properties is investigated. We present fully numerical results for the electron gas in three and two dimensions in the framework of the GW approximation. The overall agreement with very accurate Monte Carlo data is excellent, even for those ranges of densities for which the GW approach is often supposed to be unsuitable. The latter seems to be due to the fulfilment of general conservation rules. These results open further prospects for accurate calculations of ground-state properties circumventing the limitations of standard density functional theory.