The nonlocal van der Waals (NL-vdW) functionals [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] are being applied more and more frequently in solid-state physics, since they have shown to be much more reliable than the traditional semilocal functionals for systems where weak interactions play a major role. However, a certain number of NL-vdW functionals have been proposed during the last few years, such that it is not always clear which one should be used. In this work, an assessment of NL-vdW functionals is presented. Our test set consists of weakly bound solids, namely rare gases, layered systems like graphite, and molecular solids, but also strongly bound solids in order to provide a more general conclusion about the accuracy of NL-vdW functionals for extended systems. We found that among the tested functionals, rev-vdW-DF2 [Hamada, Phys. Rev. B 89, 121103(R) (2014)] is very accurate for weakly bound solids, but also quite reliable for strongly bound solids.SL/hybrid xc alone should not already lead to an overbinding, otherwise adding E NL c,disp can only make the results worse. Thus, the combination E SL/hybrid xc + E NL c,disp has to be well-balanced in order to provide accurate geometry and binding energy. 23,25,36,40 Among the NL-vdW functionals that are available in the literature, a certain number of them were selected for the present work. However, we did not consider NL-vdW functionals based on hybrid functionals, 37,38,41,42 since they lead to calculations that are much more expensive, especially for solids. They are therefore less interesting from a practical point of view as long as the electronic structure is of no particular interest. Thus, only semilocal-based NL-vdW functionals are considered and now listed.vdW-DF from Dion et al. (DRSLL), 2 the first proposed NL-vdW functional that can be applied to systems with arbitrary geometry, consists of the GGA exchange revPBE 43 (a reoptimization of PBE 14 ) and LDA correlation 44,45 for the semilocal part. The nonlocal term, Eq. (2), of the vdW-DF functional (DRSLL kernel Φ) has subsequently been used in combination with other semilocal components, and among them, those that are considered in the present work are the following four. C09-vdW from Cooper, 46 which uses a GGA (C09x) for exchange and LDA for correlation. optB88-vdW and optB86b-vdW, which are two of the functionals developed by Klimeš et al.,21,23 and use for the semilocal component, the GGAs optB88 and optB86b for exchange and LDA for correlation. Note that optB88 and optB86b are reoptimizations of B88 47 and B86b, 48 respectively. vdW-DF-cx from Berland and Hyldgaard, 25 which consists of a GGA exchange component, LV-PW86r, that is combined with LDA correlation and was constructed to be more consistent with the DRSLL kernel. vdW-DF2 from Lee et al. (LMKLL) 36 uses the GGA exchange PW86R 36 (a reoptimization of PW86 49 ) and LDA for correlation, while the kernel Φ (called LMKLL) in E NL c,disp has the same analytical form as the original DRSLL kernel, but with a reoptimized parameter Z ...

Abstract:Mapping species through classification of imaging spectroscopy data is facilitating research to understand tree species distributions at increasingly greater spatial scales. Classification requires a dataset of field observations matched to the image, which will often reflect natural species distributions, resulting in an imbalanced dataset with many samples for common species and few samples for less common species. Despite the high prevalence of imbalanced datasets in multiclass species predictions, the effect on species prediction accuracy and landscape species abundance has not yet been quantified. First, we trained and assessed the accuracy of a support vector machine (SVM) model with a highly imbalanced dataset of 20 tropical species and one mixed-species class of 24 species identified in a hyperspectral image mosaic (350-2500 nm) of Panamanian farmland and secondary forest fragments. The model, with an overall accuracy of 62%˘2.3% and F-score of 59%˘2.7%, was applied to the full image mosaic (23,000 ha at a 2-m resolution) to produce a species prediction map, which suggested that this tropical agricultural landscape is more diverse than what has been presented in field-based studies. Second, we quantified the effect of class imbalance on model accuracy. Model assessment showed a trend where species with more samples were consistently over predicted while species with fewer samples were under predicted. Standardizing sample size reduced model accuracy, but also reduced the level of species over-and under-prediction. This study advances operational species mapping of diverse tropical landscapes by detailing the effect of imbalanced data on classification accuracy and providing estimates of tree species abundance in an agricultural landscape. Species maps using data and methods presented here can be used in landscape analyses of species distributions to understand human or environmental effects, in addition to focusing conservation efforts in areas with high tree cover and diversity.

Kohn-Sham (KS) density functional theory (DFT) is a very efficient method for calculating various properties of solids as, for instance, the total energy, the electron density, or the electronic band structure. The KS-DFT method leads to rather fast calculations, however the accuracy depends crucially on the chosen approximation for the exchange and correlation (xc) functional E xc and/or potential v xc . Here, an overview of xc methods to calculate the electronic band structure is given, with the focus on the so-called semilocal methods that are the fastest in KS-DFT and allow to treat systems containing up to thousands of atoms. Among them, there is the modified Becke-Johnson potential that is widely used to calculate the fundamental band gap of semiconductors and insulators. The accuracy for other properties like the magnetic moment or the electron density, that are also determined directly by v xc , is also discussed.

The density-functional theory (DFT) approximations that are the most accurate for the calculation of bandgap of bulk materials are hybrid functionals, such as HSE06, the modified Becke–Johnson (MBJ) potential, and the GLLB-SC potential. More recently, generalized gradient approximations (GGAs), such as HLE16, or meta-GGAs, such as (m)TASK, have also proven to be quite accurate for the bandgap. Here, the focus is on two-dimensional (2D) materials and the goal is to provide a broad overview of the performance of DFT functionals by considering a large test set of 298 2D systems. The present work is an extension of our recent studies [T. Rauch, M. A. L. Marques, and S. Botti, Phys. Rev. B 101, 245163 (2020); Patra et al., J. Phys. Chem. C 125, 11206 (2021)]. Due to the lack of experimental results for the bandgap of 2D systems, G0W0 results were taken as reference. It is shown that the GLLB-SC potential and mTASK functional provide the bandgaps that are the closest to G0W0. Following closely, the local MBJ potential has a pretty good accuracy that is similar to the accuracy of the more expensive hybrid functional HSE06.

ec(h)o is an "augmented reality interface" utilizing spatialized soundscapes and a semantic web approach to information. The initial prototype is designed for a natural history and science museum. The platform is designed to create a museum experience that consists of a physical installation and an interactive virtual layer of three-dimensional soundscapes that are physically mapped to the museum displays. The source for the audio data is digital sound objects. The digital objects originate in a network of object repositories that connect digital content from one museum with other museums collections. The interface enables people to interact with the system by movement and object manipulationbased gestures without the direct use of a computer device. The focus of this paper is the retrieval mechanism for the sound objects for the museum visitor. The retrieval mechanism is built on the user model and conceptual descriptions of the sound object and museum artifacts in the form of ontologies for sound and psychoacoustics, topic ontology and Conceptual Reference Model for museum information. The retrieval criteria are represented as inference rules that represent knowledge from psychoacoustics, cognitive domain and composition aspects of interaction. The system will be demonstrated in exhibition space in Nature