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In the last decade, a large number of studies at the experimental level in electrochemical systems for energy storage devices have been performed.However, theoretical approaches are highly desirable to understand the physicochemical properties giving rise to energy storage phenomena. This work was intended to provide insights into the in silico design of novel nanocomposite materials formed by the Keggin polyoxometalate SiW12 anchored to an organic functional group ϕ − X (with X = −N H 2 , −OH, −COH and −COOH) linked to a carbon nanotube. In these systems, the Density of States around the Fermi level is enhanced, giving the composite material the capacity of facile electron transport that may be determinant at the charge/discharge cycling performed in energy storage devices. Charge trans-arXiv:1707.01435v1 [cond-mat.mtrl-sci] 5 Jul 2017 fer at the composite materials under study is greatest for the ϕ − COOH functional group, yielding an attraction with the SiW12 cluster of the same order of magnitude as that of covalent nature. The rest of the functional groups induce a non-covalent interaction of the electrostatic-type, mediated by a van der Waals attraction. Our proposed methodology may represent a tool to develop novel electrode materials that may improve the performance on energy storage devices, such as supercapacitors or Li-ion batteries.

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The use of eco-friendly materials for the environment has been addressed as a critical issue in the development of systems for renewable energy applications. In this regard, the investigation of organic photovoltaic (OPV) molecules for the implementation in solar cells, has become a subject of intense research in the last years. The present work is a systematic study at the B3LYP level of theory performed for a series of 50 OPV materials. Full geometry optimizations revealed that those systems with a twisted geometry are the most energetically stable. Nuclear independent Chemical shifts (NICS) values show a strong aromatic character along the series, indicating a possible polymerization in solid-state, via a π − π stacking, which may be relevant in the design of a solar cell device. The absorption spectra in the series was also computed using Time Dependent DFT at the same level of theory, indicating that all spectra are red-shifted along the series. This is a promissory property that may be directly implemented in a photovoltaic material, since it is possible to absorb a larger range of visible light. The computed HOMO-LUMO gaps as a measurement of the band gap in semiconductors, show a reasonable agreement with those found in experiment, predicting candidate materials that may be directly used in photovoltaic applications. Non-linear optical (NLO) properties were also estimated with the aid of a PCBM molecule as a model of an acceptor, and a final set of optimal systems was identified as potential candidates to be implemented as photovoltaic materials. The methodological approach presented in this work may aid in the in silico assisted-design of OPV materials.

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