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Lignocellulosic fibers and microcellulose have been obtained by simple alkaline treatment from softwood al- mond shells. In particular, the Prunus dulcis Miller (D.A.) Webb. was considered as a agro industrial waste largely available in southern Italy. The materials before and after purification have been characterized by 13C CPMAS NMR spectroscopy methodology. A proper data analysis provided the relative composition of lignin and holo- cellulose at each purification step and the results were compared with thermogravimetric analysis and FT-IR. To value the possibility of using this material in a circular economy framework, the fibrous cellulosic material was used to manufacture a handmade cardboard. The tensile performances on the prepared cardboard proved its suitability for packaging purposes as a sustainable material. These fibers along with the obtained microcellulose can represent a new use for the almond shells that are mainly used as firewood.

The industrial production of citrus plants for ornamental use (ornacitrus) began in Italy at the end of the 1960s due to the need for many citrus nurseries to adapt their activities in a time of crisis for citriculture. Nowadays, the ornamental citrus nursery sector is a well-established industry in many European countries such as Portugal, Spain, Greece, and southern Italy. In Italy, nursery production of ornamental citrus plants has become prominent due to the gradual shutdown of many commercial citrus orchards. Currently, Italy maintains its leadership with more than 5.5 million ornacitrus plants produced annually. Ornamental citrus production regards mainly different cultivars of Citrus and Fortunella species, with lemon as the lead species. In this paper, the contribution of breeding and cultural techniques to the innovation of the sector is reported and discussed. This review aims to give an updated scientific and technical description of a sector with large competitive potential that remains still largely unexplored, pointing out its strengths and weaknesses.

Almond cultivation in Sicily is experiencing a phase of great interest which is mainly concentrated in the development of specialized orchards, with irrigation and by adopting cultivars with high qualitative and quantitative performances. These are mostly Mediterranean genotypes with high fat content and hard or semi-hard shell, extremely different from the varieties of Californian diffusion. The development of the sector comprises the primary production of almonds but also a series of secondary products which often represent a burden for the company. From these considerations several researches have been developed with the aim of giving a value to these by-products through circular economy paths. One of the by-products widely produced, besides the shell, is the skin which covers the seed and is produced during the peeling phase. It is well-known that tegument is an important component of almond because it contains important bioactive substances (phenols and aromas) which are usually dispersed during peeling. This paper examined three different Italian cultivars widely spread in Sicily, two of Apulian origin, (Genco and Tuono), and one locally cultivated variety (Vinci a tutti). These three cultivars occupy an increasingly large area and are very popular with consumers and industry. The production of secondary products, therefore, evidences significant quantities and the possibility to give them an added value becomes a need for the sector. Therefore, the content of phenols and proanthocyanins in the skin at harvest and during storage was analyzed, adopting two different separation methods, with and without water. During the analysis it was possible to observe the different behavior of the three cultivars due to genetic and industrial factors. Skin separated without using hot water showed a higher total phenolic presence with average increases of about 20%, and with even higher increases, between 28 and 32%, for proanthocyanins. Vinci a tutti evidenced the highest total phenolic content after 8 months of storing while roasting has revealed to be a more effective skin separation approach.

Three caper (Capparis spinosa L.) biotypes grown on the Sicilian island of Salina (38&deg, 33&prime, 49&Prime, N) were micropropagated to evaluate two different in vitro culture systems: one using the traditional solid medium, and the other based on liquid culture in a PlantForm bioreactor. PlantForm is a temporary immersion system (TIS), a new propagation method in which the shoots undergo temporary immersion in a liquid medium in order to avoid the accumulation of gas through forced ventilation. This study proposes a protocol to improve the efficiency of in vitro propagation of caper plants, while also reducing production costs, because of the elimination of the gelling agent, and manual labor, requiring limited subcultures and posing minimal contamination risks. Our results show that the caper shoots propagated in bioreactors demonstrated good adaptability and better growth rates than those grown in the conventional system. Statistically significant differences were observed between plants grown in the PlantForm liquid culture and those grown in solid medium regarding the number and length of shoots, which were further promoted by the addition of plant growth regulators (PGRs). The relative growth and real proliferation rate of the caper explants were higher when using meta-Topolin than when using 6-benzylaminopurine as a PGR. Overall, the TIS improved in vitro caper culture by promoting the proliferation, length, and vigor of the shoots.

Previous research has suggested that activities such as community gardens could offer a wide range of health benefits. The aim of the article is to systematically review the available literature to analyse the magnitude of the phenomenon, the geographical distribution, and the main characteristics in terms of health outcomes and target populations. The search addresses the question whether the activity in community gardens improves health and well-being outcomes of individuals. From the total amount of 7226, 84 selected articles showed that:(1) up to 50% are published by U.S. universities or institutions; (2) up to 44% of the studies considered “community gardens” as the main activity of the research focus; (3) one-third of the studies included adults; (4) almost 25% of the studies used “general health” as the main outcome when investigating the benefits of community gardens; (5) the percentage of studies that achieved their outcomes was heterogeneous among the different health dimensions. In conclusion, while a certain degree of heterogeneity in the used definition and outcome still exist, community gardens may be a viable strategy for well-being promotion in terms of psychological, social, and physical health and may be considered as an innovative urban strategy to promote urban public health.

Almond is appreciated for its nutraceutical value and for the aromatic profile of the kernels. In this work, an almond collection composed of 96 Sicilian accessions complemented with 10 widely cultivated cultivars was phenotyped for the production of volatile organic compounds using a proton-transfer time-of-flight mass spectrometer and genotyped using the Illumina Infinium®18 K Peach SNP array. The profiling of the aroma was carried out on fresh and roasted kernels enabling the detection of 150 mass peaks. Sixty eight, for the most related with sulfur compounds, furan containing compounds, and aldehydes formed by Strecker degradation, significantly increased during roasting, while the concentration of fifty-four mass peaks, for the most belonging to alcohols and terpenes, significantly decreased. Four hundred and seventy-one robust SNPs were selected and employed for population genetic studies. Structure analysis detected three subpopulations with the Sicilian accessions characterized by a different genetic stratification compared to those collected in Apulia (South Italy) and the International cultivars. The linkage-disequilibrium (LD) decay across the genome was equal tor2 = 0.083. Furthermore, a high level of collinearity (r2 = 0.96) between almond and peach was registered confirming the high synteny between the two genomes. A preliminary application of a genome-wide association analysis allowed the detection of significant marker-trait associations for 31 fresh and 33 roasted almond mass peaks respectively. An accurate genetic and phenotypic characterization of novel germplasm can represent a valuable tool for the set-up of marker-assisted selection of novel cultivars with an enhanced aromatic profile.

Exciton band structures analysis provides a powerful tool to identify the exciton character of materials, from bulk to isolated systems, and goes beyond the mere analysis of the optical spectra. In this work, we focus on the exciton properties of molybdenum sisulfide (MoS2) by solving the ab initio many-body Bethe–Salpeter equation, as a function of momentum, to obtain the excitation spectra of both monolayer and bulk MoS2. We analyse the spectrum and the exciton dispersion on the basis of a model excitonic Hamiltonian capable of providing an efficient description of the excitations in the bulk crystal, starting from the knowledge of the excitons of a single layer. In this way, we obtain a general characterization of both bright and darks excitons in terms of the interplay between the electronic band dispersion (i.e. interlayer hopping) and the electron–hole exchange interaction. We identify for both the 2D and the 3D limiting cases the character of the lowest-energy excitons in MoS2, we explain the effects and relative weights of both band dispersion and electron–hole exchange interaction and finally we interpret the differences observed when changing the dimensionality of the system.

International audience; Dispersionless energy bands in k space are a peculiar property gathering increasing attention for the emergence of novel electronic, magnetic, and photonic properties. Here, we explore the impact of electronic flat bands on the light-matter interaction. The van der Waals interaction between the atomic layers of hexagonal boron nitride induces flat bands along specific lines of the Brillouin zone. The macroscopic degeneracy along these lines leads to van Hove singularities with divergent joint density of states, resulting in outstanding optical properties of the excitonic states. For the direct exciton, we report a giant oscillator strength with a longitudinal-transverse splitting of 420 meV, a record value, confirmed by our ab initio calculations. For the fundamental indirect exciton, flat bands result in phonon-assisted processes of exceptional efficiency, that compete with direct absorption in reflectivity, and that make the internal quantum efficiency close to values typical of direct band gap semiconductors.

We present a novel derivation of resonant inelastic x-ray scattering (RIXS) which yields an expression for the RIXS cross section in terms of emission pathways between intermediate and final many-body states. Thereby electron-hole interactions are accounted for, as obtained from full diagonalization of the Bethe-Salpeter equation within an all-electron first-principles framework. We demonstrate our approach with the emission spectra of the fluorine K edge in LiF, and provide an in-depth analysis of the pathways that determine the spectral shape. Excitoninc effects are shown to play a crucial role in both the valence and core regime.

The in vitro rooting of three caper (Capparis spinosa L.) selected biotypes, grown in a commercial orchard on the Sicilian island of Salina (38&deg, 33&prime, 49&rdquo, N), was performed using&mdash, as base material for rooting experiments&mdash, shoot explants proceeding from two different in vitro culture systems: solid medium and liquid culture in a PlantForm bioreactor (TIS). The regenerated shoots of each accession were submitted to different auxin treatments (NAA, IBA, IAA - 1 or 2 mg L&minus, &sup1, NAA+IBA 0.75 and 0.25 mg L&minus, respectively), supplemented with sucrose or fructose (mg L&minus, ). The highest rooting rate in terms of root percentage (67%) was reached with the explants of the selected accession &lsquo, Sal 39&rsquo, proceeding from liquid culture in PlantForm and induced in the MS medium with sucrose, as a carbon source, supplemented with NAA 0.75 mg L&minus, + IBA 0.25 mg L&minus, after six days in a climatic growth chamber at 25 &plusmn, 1 &deg, C in the dark and then placed under a cool white fluorescent lamp, with a PPFD of 35 &mu, mol m&minus, s&minus, and a photoperiod of 16 h. On the other hand, poor rooting rate was generally achieved under all the tested experimental conditions with the other biotypes, &lsquo, Sal 37&rsquo, and &lsquo, Sal 35&rsquo, demonstrating the strong role exerted by the previously adopted proliferation method and by the genotype for successful caper in vitro rooting.

The local fruit biodiversity can represent a good opportunity to maintain the agriculture and to develop economies in "marginal" territory such as those in the mountain rural areas. The genetic diversity of the Morus spp. is little known in the Western Pamir mountains, so that the objective of the present study was to improve the knowledge of the polymorphism of the species in the different poorly explored Tajik valleys by investigating the main quantitative and qualitative traits. Materials and methods - Six selected sites of the Gorno Badakhshan Autonomous Oblast (GBAO) region were investigated through field measurement on morphological traits of mulberry trees (both from wild and cultivated habitats). The qualitative analysis on fresh and dried fruits were carried out on four cultivars of the white mulberry (Morus alba L.) and one cultivar of the black mulberry (Morus nigra L.) collected in the Pamir Biological Institute, the highest botanical garden of the Commonwealth of Independent States (CIS). Results and discussion - Our study revealed high variability for all the measured parameters confirmed by a wide polymorphism. The highest rate of variability and the most promising genotypes in terms of fruit morphological traits were observed in the Vanch and the Rushan valleys. Due to the highest ascorbic acid content for the black cv. Shatut and the white cv. Marvori and a better taste, confirmed by the highest reducing and total sugar contents during the early and the full ripening (cv. Bedonia), mulberry fruits can be suggested for the fresh consumption. The cv. Shatut is the only one suggested for sun-drying, following specific local recipes for traditional consumption. Conclusion - The high morphogenetic variability of the mulberry trees in a marginal mountain area as the Gorno Badakhshan in the Western Pamir offers opportunities to make value of fruits with high nutritional and sensory profile and to develop the agricultural resources of any vulnerable territory.

A growing awareness that highly intensified agricultural systems have made a substantial worldwide contribution to the worsening of the resilience capacity of natural ecosystems has, over the last twenty years, brought general attention to agroecological management models. This aspect is even more evident in industrial agriculture, which is based on the use of multiple chemical products derived from non-natural synthesis. In more developed countries, a new idea of ecology linked to agricultural production has been increasingly developed and, for this reason, there has been a greater diffusion of differentiated agricultural models taking into consideration the environmental impact of production choices and policies addressed to the conservation of natural resources. In urban agricultural production, it is even more important to adopt resilient production models that, in addition to developing responsible production paths and allowing a positive connection with the needs of consumers, guarantees reasonable and positive behaviors respecting the environment in which most of the urban population lives; in other words, the implementation of goal 12 of the sustainable development goals (SDG #12 Responsible Production and Consumption) of the United Nations. In this work, we report some case studies inspired by the activities carried out by the Slow Food Association in Africa and demonstrate the importance of agroecological models in small-scale agricultural systems, related to the development of school and community gardens in small urban areas of different African countries, as a tool for integrating agricultural activities aimed at social resilience and the conservation of ecosystems.

International audience; The dynamic structure factor of materials is proportional to their linear electronic response and it displays their excitation spectra. Usually the response is measured on the same length scale as the perturbation. Here we illustrate that much can be gained by studying also the mixed dynamic structure factor, which connects different spatial components of perturbation and response. We extend state-of-the-art ab initio calculations to access the mixed dynamic structure factor, including excitonic effects. Using bulk silicon and lithium fluoride as prototype examples, we show that these effects play a crucial role above and below the quasi-particle gap, and are needed in order to explain coherent inelastic x-ray scattering experiments. Our approach also yields important information concerning the microscopic structure of time-dependent density functional theory. One of the key concepts in condensed matter theory is screening, the modification of a potential felt by a charge due to the rearrangement of other charges [1]. In many cases the dominant contribution to this phenomenon can be described in linear response [2]. This means that the knowledge of the response of a system to an external perturbation is entirely contained in the density-density response function χ,which is determined only by the material.The poles of χ in frequency space are the excitation energies of the system. The density-density response function is measured directly or indirectly in many spectroscopy experiments [3], such as electron energy loss spectroscopy (EELS) [4], optical absorption [5, 6], or inelastic x-ray scattering (IXS) [7], which yields the dynamic structure factor (DSF) that is proportional to the imaginary part of χ. Knowing χ can also help to understand or predict effects such as a significant local rearrangement of charges as response of the system to a perturbation, which can have dramatic effects on the structure, for example self-trapped excitons [8]. Finally, screening is also one of the fundamental processes that govern the behavior of all many-body systems. Therefore it appears naturally as a building block in the formulation of many-body perturbation theory [9], via the screened Coulomb interaction W = v c + v c χv c , where v c is the bare Coulomb interaction. The widely-used GW approximation (GWA) [10], for example, uses W as effective interaction. Some important features of the frequency-dependent screening are captured for the homogeneous electron gas by the Lindhard dielectric function [11] from the random phase approximation (RPA) [12], where only the classical electrostatic potential between charges is taken into account. For small momentum transfer this is sufficient to describe the long-range collective oscillations of the electron gas, called plasmons, even for simple metals and semiconductors (see, e.g., [13-17]). However, in many other cases this approximation yields unsatisfactory results. Prominent examples are materials with localized d-or f-states [18-21], or loss spectra for larger momentum transfer [22-25], where a shorter length scale is probed. Moreover, the RPA cannot yield bound ex-citons [26], which are most clearly seen in optical spectra [27, 28]. Such many-body effects are instead captured by the Bethe-Salpeter equation (BSE) [29], a two-body Dyson equation that correlates the excited electrons and holes [26, 30]. This equation has been successfully used to calculate optical spectra in the framework of semi-empirical calculations since the eighties [31-34], and in first principles calculations since the nineties [35-38]. Loss spectra for vanishing momentum transfer have been looked at more recently [39-41], and a few calculations exist for loss spectra at non-vanishing momentum transfer [42-50]. Optics, EELS and IXS probe the response of the system on the same length scale as the perturbation. Besides the spectroscopic information, this allows one also to reconstruct charge excitations as an averaged function of space and time from experimental IXS spectra [51-55]. However, in an inhomogeneous material even a spatially monochromatic perturbation creates a response on different length scales [56, 57], depending on the local structure of the material. Only when all these components of the response are known can one describe induced charges with spatial resolution, and can one determine important many-body effects that depend on all the components of W. For these reasons, it is highly desirable to extend state-of-the-art advanced theoretical and numerical approaches to the description of the full inhomogeneous response of materials including excitonic effects. This gives access to the mixed DSF (MDSF), which is a matrix in reciprocal space whose diagonal is the ordinary DSF [7]. The MDSF can be measured by coherent IXS (CIXS) [7]. On the theory side, some off-diagonal elements of the MDSF in silicon were calculated in the adiabatic local density approximation (ALDA) of time-dependent den

International audience; We perform a systematic study of the macroscopic dielectric function and electron energy loss (EEL) spectra for graphite. We obtain the dispersion behavior for the π plasmon, as a function of the momentum transfer q for two nonequivalent paths that traverse the first four Brillouin zones. We carry out these calculations within both time-dependent density functional theory (with two exchange-correlation functionals) and the Bethe-Salpeter equation. Additionally, we explore the effects of using the complete excitonic Hamiltonian (with all electron-hole pairs and antipairs), and within the Tamm-Dancoff approximation (neglecting antipairs). By analyzing the behavior of the macroscopic dielectric function, we are able to determine which peaks are predominantly from plasmonic behavior or only interband transitions. We compare the calculated spectra against several experiments that span almost five decades; our results present clear trends that follow the physical origins of the observed peaks. We carry out this study over a large range of momentum transfer in order to better evaluate the different theoretical methods compared to experiment, and predict the plasmonic behavior beyond available experimental data. Our results indicate that including the complete Hamiltonian with the exciton coupling included is essential for accurately describing the observed EEL spectra and plasmon dispersion of graphite, particularly for low values of momentum transfer. However, the solution of the Bethe-Salpeter equation is computationally intensive, so time-dependent density functional theory methods used in conjunction with the complete Hamiltonian may be an attractive alternative.

This work proposes for the first time a model for reusing almond (Prunus dulcis cv. Casteltermini from Sicily, Southern Italy) skin to formulate a new functional blackberry (Rubus ulmifolius Schott) jam. For this purpose, blackberries were analysed fresh and as jam, traditionally prepared with a minimum fruit amount of 80%. Different percentages of almond skin (20, 15, and 10% w/w) were added to jam. The phytochemical profile of enriched jam was investigated by LC-ESI/LTQOrbitrap/MS analyses. Anthocyanins, hydrolysable tannins, and triterpenoids were identified in a blackberry extract, while proanthocyanidins, flavonoids, and oxylipins were identified in an almond extract. The n-hexane extract of P. dulcis skin, investigated by GC–MS, evidenced linoleic, palmitic, and oleic acids as the main abundant compounds. Samples were investigated for their antioxidant activity using DPPH, ABTS, β-carotene, and FRAP tests. The hypoglycaemic and hypolipidemic effects were studied by α-amylase, α-glucosidase, and lipase inhibitory assays. In order to evaluate the effect of thermal process on enriched jam bioactivity, pasteurisation was applied. An increase in activities for all samples was observed, in particular for jam enriched with 20% w/w of almond skin. Based on obtained data, and supported by sensory analysis, we propose enriched jam as a promising source of compounds useful for preventing diseases associated with oxidative stress.

Rural development policies today include significant directions towards ecological transition and sustainability. Biodiversity plays a fundamental role, especially in fragile environments. The North African oases, for example, are socio-ecological structures with delicate balances in terms of natural resources, where the activation of participatory conservation approaches appears today to be very useful, aiming at long-lasting results. This type of approach was applied in the oasis of El Hamma, in Tunisia. The socio-ecological analysis was carried out through semi-structured interviews with different stakeholders of the oasis. The results were used to activate focus groups and to identify, in a participatory way, a conservation strategy for the species and the varieties at risk of erosion or disappearing. From this research, a wide spread of non-traditional date palm and vegetables emerged in a very diverse social context. These products were recognized as highly significant in terms of traditional knowledge by all stakeholders. Therefore, a Maison des semences and a public conservation center for perennial species were created, representing the first step of a participatory conservation model. Seeds of 11 traditional annual species, 10 date palm varieties and, in perspective, many other fruit species and vegetable varieties have been introduced into conservation.

A sustainable future for the community is one of the objectives established by the European Union Agenda 2030. Furthermore, sustainable consumption has been identified as one of the possible trajectories for sustainable development. It is for this reason that food production, distribution and consumption ways cannot be overlooked for sustainability achievement, as well as the consumer&rsquo, s related perception. In this research the Best&ndash, Worst scaling methodology was adopted to explore the priorities declared by a sample of 801 consumers among 12 different sustainability definitions selected from the scientific literature. The choice experiment was carried out through face-to-face interviews during two food and wine events closely related to the sustainability theme in the food sector. The respondents considered as sustainability priority definition the &ldquo, preservation of natural resources&rdquo, followed by &ldquo, decent working conditions&rdquo, and &ldquo, accessibility for everyone to healthy and safe food&rdquo, Moreover, 5 consumer&rsquo, s clusters were identified according to the priorities assigned to the different sustainability definitions, as well as to individuals socio-demographic characteristics. The description of the priorities assigned by the clusters to the different sustainability definitions have also been described as guidelines for consumer attitudes towards the different sustainability dimensions (environmental, social, economic and governance).

Gianni S., Sottile F. (2015): In vitro storage of plum germplasm by slow growth . Hort. Sci. (Prague), 42: 61–69. In this study, in vitro slow growth storage was investigated in four cultivars of two Sicilian (Southern Italy) plum species (Prunus domestica L. and Prunus cerasifera Ehrh. – two genotypes each). Established shoot cultures were preserved at 4°C in the dark in a Murashige and Skoog basal medium containing one of two different concentrations of sucrose (20 and 30 g/l) and with or without growth regulators. We tested the effects of cold storage, genotype and media on survival and re-growth capacity of explants after 3, 6, 9 and 12 months of storage. Effective minimal growth under cold conditions occurred in all four genotypes. The media composition did not affect survival, which, instead, appeared to be genotype-dependent. P. domestica genotypes survived cold storage the longest, for 12 and 9 months; instead, P. cerasifera ones remained viable for up to 6 months. All genotypes retained proliferation capacity under standard conditions and their re-growth capacity seems to be strongly genotype-dependent, closely related to their individual performance in response to the experimental condition of storage.

Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d-d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material. Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d-d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material. Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d-d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material.

International audience; A promising route towards nanodevice applications relies on the association of graphene and transition metal dichalcogenides with hexagonal boron nitride (h-BN). Due to its insulating nature, h-BN has emerged as a natural substrate and gate dielectric for graphene-based electronic devices. However, some fundamental properties of bulk h-BN remain obscure. For example, the band structure and the position of the Fermi level have not been experimentally resolved. Here, we report a direct observation of parabolic dispersions of h-BN crystals using high-resolution angle-resolved photoemission spectroscopy (ARPES). We find that h-BN exfoliation on epitaxial graphene enables overcoming the technical difficulties of using ARPES with insulating materials. We show trigonal warping of the intensity maps at constant energy. The valence-band maxima are located around the K points, 2.5 eV below the Fermi level, thus confirming the residual p-type character of typical h-BN.

We present a general picture of the exciton properties of layered materials in terms of the excitations of their single-layer building blocks. To this end, we derive a model excitonic hamiltonian by drawing an analogy with molecular crystals, which are other prototypical van der Waals materials. We employ this simplified model to analyse in detail the excitation spectrum of hexagonal boron nitride (hBN) that we have obtained from the {\it ab initio} solution of the many-body Bethe-Salpeter equation as a function of momentum. In this way we identify the character of the lowest-energy excitons in hBN, discuss the effects of the interlayer hopping and the electron-hole exchange interaction on the exciton dispersion, and illustrate the relation between exciton and plasmon excitations in layered materials., Accepted for Phys. Rev. B

School gardens are, increasingly, an integral part of projects aiming to promote nutritional education and environmental sustainability in many countries throughout the world. In the late 1950s, FAO (Food and Agriculture Organization) and UNICEF (United Nations Children's Fund) had already developed projects to improve the dietary intake and behavior through school and community gardens. However, notwithstanding decades of experience, real proof of how these programs contribute to improving sustainability has not been well-documented, and reported findings have mostly been anecdotal. Therefore, it is important to begin a process of collecting and monitoring data to quantify the results and possibly improve their efficiency. This study’s primary goal is to propose an interpretive structure—the “Sustainable Agri-Food Evaluation Methodology-Garden” (SAEMETH-G), that is able to quantifiably guide the sustainability evaluation of various school garden organizational forms. As a case study, the methodology was applied to 15 school gardens located in three regions of Kenya, Africa. This application of SAEMETH-G as an assessment tool based on user-friendly indicators demonstrates that it is possible to carry out sustainability evaluations of school gardens through a participatory and interdisciplinary approach. Thus, the hypothesis that the original SAEMETH operative framework could be tested in gardens has also been confirmed. SAEMETH-G is a promising tool that has the potential to help us understand school gardens’ sustainability better and to use that knowledge in their further development all over the world.

International audience; We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia (m-HfO$_2$) obtained from time-dependent density-functional theory (TDDFT) predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope. Fermi's Golden Rule density-functional theory (DFT) calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. Using the DFT density of states and TDDFT dielectric functions, we characterize the excitations that result in the m-HfO$_2$ energy loss spectrum. The sole plasmon occurs between 13-16 eV, although the peaks $\sim$28 and above 40 eV are also due to collective excitations. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons (5$p$ and 4$f$) on the energy-loss spectrum, and find that the inclusion of transitions from the 4$f$ band damps the energy-loss intensity in the region above 13 eV. We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation (ALDA) exchange-correlation kernel, as well as from a many-body perspective using a $GW$-derived electronic structure to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf $4f$ shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks.

International audience; Low-dimensional materials differ from their bulk counterpart in many respects. In particular, thescreening of the Coulomb interaction is strongly reduced, which can have important consequencessuch as the significant increase of exciton binding energies. In bulk materials the binding energyis used as an indicator in optical spectra to distinguish different kinds of excitons, but this is notpossible in low-dimensional materials, where the binding energy is large and comparable in size forexcitons of very different localization. Here we demonstrate that the exciton band structure, whichcan be accessed experimentally, instead provides a powerful way to identify the exciton character.By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane andsingle-layer hexagonal BN, we draw a general picture of the exciton dispersion in two-dimensionalmaterials, highlighting the different role played by the exchange electron-hole interaction and by theelectronic band structure. Our interpretation is substantiated by a prediction for phosphorene.

A major obstacle for computing optical spectra of solids is the lack of reliable approximations for capturing excitonic effects within time-dependent density-functional theory. We show that the trustful prediction of strongly bound electron-hole pairs within this framework using simple approximations is still a challenge and that available promising results have to be revisited. Deriving a set of analytical formula we analyze and explain the difficulties. We deduce an alternative approximation from an iterative scheme guided by previously available knowledge, significantly improving the description of exciton binding energies. Finally, we show how one can "read" exciton binding energies from spectra determined in the random phase approximation, without any further calculation., Comment: 5 pages, 2 figures plus supplemental material

The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe-Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators., This research was supported by a Marie Curie FP7 Integration Grant within the 7th European Union Framework Programme. Computational time was granted by GENCI (Project No. 544). We also acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010- AdG-267374), Spanish Grant (FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13) and European Community FP7 project CRONOS (Grant number 280879-2) and COST Actions CM1204 (XLIC) and MP1306 (EUSpec).

Classical Hartree effects contribute substantially to the success of time-dependent density functional theory, especially in finite systems. Moreover, exchange-correlation contributions have an asymptotic Coulomb tail similar to the Hartree term, and turn out to be crucial in describing response properties of solids. In this work, we analyze in detail the role of the long-range part of the Coulomb potential in the dielectric response of finite and infinite systems, and elucidate its importance in distinguishing between optical and electron energy loss spectra (in the long wavelength limit q--0). We illustrate numerically and analytically how the imaginary part of the dielectric function and the loss function coincide for finite systems, and how they start to show differences as the distance between objects in an infinite array is decreased (which simulates the formation of a solid). We discuss calculations for the model case of a set of interacting and noninteracting beryllium atoms, as well as for various realistic systems, ranging from molecules to solids, and for complex systems, such as superlattices, nanotubes, nanowires, and nanoclusters., This work was funded in part by the EU’s RTN NANOPHASE, the EU’s 6th Framework Programme through the NANOQUANTA Network of Excellence (NMP4-CT-2004-500198), the French “Ministère de la recherche” in the framework of the “ACI Nanostructures,” Spanish DGES, Basque Country University, and Iberdrola S.A. The work of L. K. D. was funded by the joint research program “ISMIR” between CEA and CNRS. Calculations have been done using ABINIT (http://www.abinit.org/), PWSCF (http://www.pwscf.org/), LSI-CP, and LSI-DP (http://theory.polytechnique.fr/codes/). Computer time was granted by IDRIS (project 000544) and by CEA/DSM on the cluster of Compaq Alphaserver (project p543) and NEC SX6 (project p93). A. R. acknowledges support from the Salvador Madariaga program of the Ministry of Science and Education of Spain for a sabbatical leave at the Ecole Polytechnique where this work was started.

Wireless sensor networks (WSNs) are a key part of the Internet of Things vision which aims at bridging together the physical and the digital worlds in several application domains. In the building automation field, WSNs are widely adopted for energy optimization, safety and security purposes, and could greatly benefit from existing information already available in preexisting building information models (BIMs). Such BIMs are normally developed during the building design phase and reused continuously during the construction and operation phases of the building life-cycle. In current deployments, however, due to lack of interoperability such information (e.g., walls geometry, materials, and so on) must often be recollected and reinputed by WSN commissioning specialists. Open development and planning tools and methodologies can play a key role in fostering interoperability and convergence of BIM and WSN systems. This paper aims at demonstrating how increased interoperability between WSN development-support tools and BIM systems could provide advantages to developers, integrators, domain specialist, and BIM users. The methodology is validated by applying a newly proposed tool exploiting BIM interoperability to support the planning of the topology of a WSN based on ultrawideband technologies. The proposed approach is evaluated through a small-scale experimentation held in a historical building in Torino (Italy).

By solving the many-body Bethe-Salpeter equation at finite momentum transfer, we characterize the exciton dispersion in two prototypical molecular crystals, picene and pentacene, in which localized Frenkel excitons compete with delocalized charge-transfer excitons. We explain the exciton dispersion on the basis of the interplay between electron and hole hopping and electron-hole exchange interaction, unraveling a simple microscopic description to distinguish Frenkel and charge-transfer excitons. This analysis is general and can be applied to other systems in which the electron wave functions are strongly localized, as in strongly correlated insulators., The authors acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374), Spanish grants (2010-21282-C02-01 and PIB2010US-00652), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13), European Commission projects CRONOS (Grant No. 280879-2 CRONOS CP-FP7), and the Maison de la simulation for technical support. Computational time was granted by GENCI (Project No. 544) and by the CNANO-SIMULEE-2009 project. This work was carried out under the HPC-EUROPA2 project, with the support of the European Community–Research Infrastructure Action of the FP7

We present a scheme to calculate exciton dispersions in real materials that is based on the first-principles many-body Bethe-Salpeter equation. We assess its high level of accuracy by comparing our results for LiF with recent inelastic x-ray scattering experimental data on a wide range of energy and momentum transfer. We show its great analysis power by investigating the role of the different electron-hole interactions that determine the exciton band structure and the peculiar “exciton revival” at large momentum transfer. Our calculations for solid argon are a prediction and a suggestion for future experiments. These results demonstrate that the first-principles Bethe-Salpeter equation is able to describe the dispersion of localized and delocalized excitons on equal footing and represent a key step for the ab initio study of the exciton mobility., We acknowledge financial support from Triangle de la Physique 2013-0013T IXST, the ERC Advanced Grant DYNamo (No. ERC-2010-AdG-267374), Spanish Grants (No. 2010-21282-C02-01 and No. PIB2010US-00652),Grupos Consolidados UPV/EHU del GobiernoVasco (Grant No. IT578-13) and European Commission projects CRONOS (Grant No. 280879-2 CRONOS CP-FP7). Computational time was granted by GENCI (Project No. 544) and by the CNANO-SIMULEE-2009 project.

We present experimental data and theoretical results for valence-band satellites in semiconductors, using the prototypical example of bulk silicon. In a previous publication we introduced a new approach that allows us to describe satellites in valence photoemission spectroscopy, in good agreement with experiment. Here we give more details; we show how the the spectra change with photon energy, and how the theory explains this behaviour. We also describe how we include several effects which are important to obtain a correct comparison between theory and experiment, such as secondary electrons and photon cross sections. In particular the inclusion of extrinsic losses and their dependence on the photon energy are key to the description of the energy dependence of spectra.

PACS numbers: 71.45.Gm, 71.10. w, 71.15.Qe.-- et al., The experimental valence band photoemission spectrum of semiconductors exhibits multiple satellites that cannot be described by the GW approximation for the self-energy in the framework of many-body perturbation theory. Taking silicon as a prototypical example, we compare experimental high energy photoemission spectra with GW calculations and analyze the origin of the GW failure. We then propose an approximation to the functional differential equation that determines the exact one-body Green's function, whose solution has an exponential form. This yields a calculated spectrum, including cross sections, secondary electrons, and an estimate for extrinsic and interference effects, in excellent agreement with experiment. Our result can be recast as a dynamical vertex correction beyond GW, giving hints for further developments. © 2011 American Physical Society., We acknowledge support by ANR (NT09-610745), St Gobain R&D (091986), and Triangle de la Physique (2007-71). J.J.R. and J.J.K. are also supported in part by DOE BES Grant DE-FG03-97ER45623 and DOE CMCSN. Computer time was granted by IDRIS (544).

International audience; We present a method for the evaluation of electronic excitations of advanced materials by reformulating spectral sum-over-states expressions such that only occupied states appear. All empty states are accounted for by one effective energy. Thus we keep the simplicity and precision of the sum-over-states approach while speeding up calculations by more than an order of magnitude. We demonstrate its power by applying it to the GW method, where a huge summation over empty states appears twice (screening and self-energy). The precision is shown for bulk Si and solid and atomic Ar. We then use it to determine the band gap of the technologically important oxide SnO2.

We present a detailed investigation of the dynamic structure factor $S(\mathbf{Q},\ensuremath{\omega})$ as well as of the dielectric function ${\ensuremath{\epsilon}}_{\text{M}}(\mathbf{Q},\ensuremath{\omega})$ of the prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering measurements and ab initio calculations. We show that, in contrast to optical spectra, for finite momentum transfer, time-dependent density-functional theory in adiabatic local-density approximation (TDLDA) together with the inclusion of lifetime effects in a modified independent-particle polarizability ${\ensuremath{\chi}}^{0,\text{LT}}$ describes the physics of valence excitations with high precision. This applies to the dynamic structure factor as well as to the dielectric function, which demonstrates that TDLDA contains the short-range many-body effects that are crucial for a correct description of ${\ensuremath{\epsilon}}_{\text{M}}(\mathbf{Q},\ensuremath{\omega})$ in silicon at finite momentum transfer. The form of a nonlocal and energy-dependent exchange-correlation kernel is presented which provides the inclusion of the lifetime effects using the true independent-particle polarizability ${\ensuremath{\chi}}^{0}$. The description of the silicon ${L}_{2,3}$ absorption edge has been possible by including the outer core electrons $2s$ and $2p$ in the valence electrons of the pseudopotential. The energy of the edge is underestimated but a scissor shift of the respective states by the self-energy correction for these states yields good agreement with experiment. Short-range crystal local-field effects and exchange-correlation effects become important with increasing momentum transfer. The inclusion of crystal local-field effects in the random-phase approximation is able to describe the anisotropy of the response well. Our results demonstrate the quantitative predictive power of the first-principles description.

Time-dependent density-functional theory (TDDFT) is widely used in the study of linear response properties of finite systems. However, there are difficulties in properly describing excited states, which have double- and higher-excitation characters, which are particularly important in molecules with an open-shell ground state. These states would be described if the exact TDDFT kernel were used; however, within the adiabatic approximation to the exchange-correlation (xc) kernel, the calculated excitation energies have a strict single-excitation character and are fewer than the real ones. A frequency-dependent xc kernel could create extra poles in the response function, which would describe states with a multiple-excitation character. We introduce a frequency-dependent xc kernel, which can reproduce, within TDDFT, double excitations in finite systems. In order to achieve this, we use the Bethe-Salpeter equation with a dynamically screened Coulomb interaction W(omega), which can describe these excitations, and from this we obtain the xc kernel. Using a two-electron model system, we show that the frequency dependence of W does indeed introduce the double excitations that are instead absent in any static approximation of the electron-hole screening.

[EN]: The suitability of the time-dependent density-functional theory (TDDFT) approach for the theoretical study of the optical properties of biomolecules is demonstrated by several examples. We critically discuss the limitations of available TDDFT implementations to address some of the present open questions in the description of the excited-state dynamics of biological complexes. The key objective of the present work is to address the performance of TDDFT in the linear response regime of the bio-molecular systems to the visible or near UV radiation - measured by, e.g. optical absorption or optical dichroism spectra. Although these spectra are essentially determined by the electronic degrees of freedom of small, optically active regions within the usually large biological systems, they can also be strongly influenced by environment effects (solvent, hosting protein, temperature, etc.). Moreover, many key biological processes consist of photo-induced dynamics (photoisomerisation, etc.), and their description requires a coupled treatment of electronic and nuclear degrees of freedom. We illustrate these aspects with a selection of paradigmatic biomolecular systems: chromophores in fluorescent proteins, porphyrins, DNA basis, the azobenzene dye, etc. To cite this article: A. Castro et al., C. R. Physique 10 (2009). © 2008., We acknowledge funding by the Deutsche Forschungsgemeinschaft through SPP 1093 and SFB 658, Spanish MEC (FIS2007-65702-C02-01) and Grupos Consolidados UPV/EHU of the Basque Country Government (2007), by the European Community through NoE Nanoquanta (NMP4-CT-2004-500198), SANES (NMP4-CT-2006-017310), ANR (Project NT0S-3_43900), DNA-NANODEVICES (IST-2006-029192) and NANO-ERA Chemistry projects, UPV/EHU (SGIker Arina) and the European Community through e-I3 ETSF project (Contract Number 211956). M.A.L.M. acknowledges partial support by the Portuguese FCT through the project PTDC/FIS/73578/2006.

7 pages, 8 figures, 2 tables., We present a theoretical investigation of electronic and optical properties of free-base porphyrins based on density functional theory and many-body perturbation theory. The electronic levels of free-base porphine (H2P) and its phenyl derivative, free-base tetraphenylporphyrin (H2TPP) are calculated using the ab initio GW approximation for the self-energy. The approach is found to yield results that compare favorably with the available photoemission spectra. The excitonic nature of the optical peaks is revealed by solving the Bethe–Salpeter equation, which provides an accurate description of the experimental absorption spectra. The lowest triplet transition energies are in good agreement with the measured values., We acknowledge funding by the European Community through e-I3 ETSF project (INFRA-2007-1.2.2: Grant Agreement No. 211956) and by the Spanish MEC ( Grant No. FIS2007-65702-C02-01 ), “Grupos Consolidados UPV/EHU del Gobierno Vasco” (Grant No. IT-319-07), CSIC and by MIUR-PRIN2007.

International audience; The electron energy-loss function of graphite is studied for momentum transfers q beyond the first Brillouin zone. We find that near Bragg reflections the spectra can change drastically for very small variations in q. The effect is investigated by means of first principle calculations in the random phase approximation and confirmed by inelastic x-ray scattering measurements of the dynamic structure factor S(q,ω). We demonstrate that this effect is governed by crystal local field effects and the stacking of graphite. It is traced back to a strong coupling between excitations at small and large momentum transfers.

International audience; We have measured a strictly linear pi-plasmon dispersion along the axis of individualized single wall carbon nanotubes, which is completely different from plasmon dispersions of graphite or bundled single wall carbon nanotubes. Comparative ab initio studies on graphene based systems allow us to reproduce the different dispersions. This suggests that individualized nanotubes provide viable experimental access to collective electronic excitations of graphene, and it validates the use of graphene to understand electronic excitations of carbon nanotubes. In particular, the calculations reveal that local field effects (LFE) cause a mixing of electronic transitions, including the 'Dirac cone', resulting in the observed linear dispersion.

We present calculations of the absorption spectrum of semiconductors and insulators comparing various approaches: (i) the two-particle Bethe-Salpeter equation of many-body perturbation theory; (ii) time-dependent density-functional theory using a recently developed kernel that was derived from the Bethe-Salpeter equation; and (iii) a mapping scheme that we propose in the present work and that allows one to derive different parameter-free approximations to (ii). We show that all methods reproduce the series of bound excitons in the gap of solid argon, as well as continuum excitons in semiconductors. This is even true for the simplest static approximation, which allows us to reformulate the equations in a way such that the scaling of the calculations with the number of atoms equals the one of the random phase approximation.

We show the application of an efficient numerical scheme to obtain the independent-particle dynamic polarizability matrix chi((0))(r,r('),omega), a key quantity in modern ab initio excited-state calculations. The method has been applied to the study of the optical response of a realistic oxidized silicon surface, including the effects of crystal local fields. The latter are shown to substantially increase the surface optical anisotropy in the energy range below the bulk band gap. Our implementation in a large-scale ab initio computational code allows us to make a quantitative study of the CPU time scaling with respect to the system size, and demonstrates the real potential of the method for the study of excited states in large systems.

In the description of the interaction between electrons beyond the classical Hartree picture, bare exchange often yields a leading contribution. Here we discuss its effect on optical spectra of solids, comparing three different frameworks: time-dependent Hartree-Fock, a recently introduced combined density-functional and Green's functions approach applied to the bare exchange self-energy, and time-dependent exact-exchange within time-dependent density-functional theory (TD-EXX). We show that these three approximations give rise to identical excitonic effects in solids; these effects are drastically overestimated for semiconductors. They are partially compensated by the usual overestimation of the quasiparticle band gap within Hartree-Fock. The physics that lacks in these approaches can be formulated as screening. We show that the introduction of screening in TD-EXX indeed leads to a formulation that is equivalent to previously proposed functionals derived from Many-Body Perturbation Theory. It can be simulated by reducing the long-range part of the Coulomb interaction: this produces absorption spectra of semiconductors in good agreement with experiment., Comment: 12 pages, 3 figures, 1 table

Time-dependent density functional theory faces an important problem when it comes to extended systems: The long-range component of the exchange-correlation kernel ${f}_{\mathrm{xc}}$ is completely absent from local density or generalized gradient approximations, but it is believed to be present in the ``exact'' ${f}_{\mathrm{xc}}$. Several attempts have been made to solve this issue, the simplest of them being the use of a model static long-range kernel of the form $\ensuremath{-}{\ensuremath{\alpha}}^{\mathrm{static}}∕{q}^{2}$. In this paper, we propose and motivate a dynamical extension of this model of the form $\ensuremath{-}(\ensuremath{\alpha}+\ensuremath{\beta}{\ensuremath{\omega}}^{2})∕{q}^{2}$. The dynamical model is then used to calculate the dielectric function of a large variety of semiconductors and insulators. The absorption spectra of large gap insulators are remarkably improved with respect to calculations where the kernel is taken to be static. This approach is valid also for energies in the range of plasmons, and hence it yields, e.g., good electron energy loss spectra. Finally, we present some simple theoretical arguments that relate the parameters of the model to physical quantities, like the dielectric constant and the plasmon frequency.

We propose an alternative formulation of Many-Body Perturbation Theory that uses the density-functional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, that leads to excellent optical absorption and energy loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for any level of approximation. Moreover, we show the direct impact of this formulation on the time-dependent density-functional theory. Numerical results for the band gap of bulk silicon and solid argon illustrate corrections beyond the GW approximation for the self-energy., Comment: 4 pages, in press on Phys. Rev. Lett

et al., We discuss the effects of a static long-range contribution -α/q2 to the exchange-correlation kernel fxc(q) of time-dependent density functional theory. We show that the optical absorption spectrum of solids exhibiting a strong continuum excitonic effect is considerably improved with respect to calculations where the adiabatic local-density approximation is used. We discuss the limitations of this simple approach, and in particular that the same improvement cannot be found for the whole spectral range including the valence plasmons and bound excitons. On the other hand, we also show that within the range of validity of the method, the parameter α depends linearly on the inverse of the dielectric constant, and we demonstrate that this fact can be used to predict continuum excitonic effects in semiconductors. Results are shown for the real and imaginary part of the dielectric function of Si, GaAs, AlAs, diamond, MgO, SiC and Ge, and for the loss function of Si., This work was supported in part by the European Community Contract No. HPRN-CT-2000-00167, and by the French ‘‘Ministère de Recherche’’ in the framework of the program ‘‘ACI Nanostructures’’ under the Contract No. N52-01.

The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO$_2$) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO$_2$, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO$_2$ may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.

International audience; The Kohn-Sham system is the prototypical example of an auxiliary system that targets, in principle exactly, an observable like the electronic density without the need to calculate the complicated many-body wavefunction. Although the Kohn-Sham system does not describe excited-state properties directly, it represents a very successful strategy guideline also for many spectroscopy applications. Here we propose a generalization of the Kohn-Sham idea. In many situations one is interested only in limited answers to specific questions, whereas in state-of-the-art approaches a lot of information is generally calculated that is not needed for the interpretation of experimental spectra. For example, while the target is a spectrum S(ω) like the optical absorption of a solid, within time-dependent density-functional theory (TDDFT) one calculates the whole response function χ(r, r , ω). Analogously , within many-body perturbation theory (MBPT) one calculates the whole one-particle Green's function G(r, r , ω), while only the total spectral function A(ω) is needed for angle-integrated pho-toemission spectra. In this contribution, we advocate the possibility to design auxiliary systems with effective potentials or kernels that target only the specific spectral properties of interest and are simpler than the self-energy of MBPT or the exchange-correlation kernel of TDDFT. In particular, we discuss the fundamentals and prototypical applications of simplified effective kernels for optical absorption and spectral potentials for photoemission, and we discuss how to express these potentials or kernels as functionals of the density.