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The composition and structure of Calcium-Silicate-Hydrate (C-S-H) phases depends on various reaction parameters leading to its formation. Molecular Dynamic simulation studies probing the formation and structure of C-S-H are generally computationally expensive and can reach only very short time scales. Herein, we propose a coarse graining approach to model the formation of C-S-H, using patchy particles and a modified Patchy Brownian Cluster Dynamics algorithm. The simulations show that patchy particle systems can recover the qualitative kinetic evolution of C-S-H formation, and the obtained final structures were comparable to previously reported molecular dynamics studies and experiments. The model was extended to study the effect of water in the polymerization of tetraethoxysilane oligomers, the principal component of an impregnation treatment for deteriorated concrete surfaces. The intermediate system properties predicted by the simulations, such as viscosity and gel time, and structure were found to be well in accordance with the tailored experiments., The work described in this manuscript has been performed under InnovaConcrete EC project, supported by funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement N° 760858. AP and JSD also acknowledge the support received from the BASKRETE initiative and the Joint Transborder Laboratory (LTC) “Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials”.

The last generation of cement hydration accelerators relies on the seeding effect induced by amorphous calcium silicate hydrate particles. However, little is known about the effect of variables, such as the degree of crystallinity and morphology, on their performance. In this work, particles with a Ca/(Si+Al) molar ratio of 0.83 and different proportions of aluminum substitution for silicon were synthesized under hydrothermal conditions. X-ray diffractograms, nuclear magnetic resonance spectra, and scanning electron microscopy images showed that this altered the degree of crystallinity, structure, and morphology of the particles. Nevertheless, the addition of the synthesis products to cement pastes and their subsequent study by isothermal calorimetry and mechanical tests showed that the variables with the largest impact on cement hydration are the dosage and the proper dispersion of the particles. In fact, the use of a dispersing agent is highly recommended while drying of the particles should be avoided to prevent irreversible agglomeration processes from taking place., This study was carried out under the umbrella of the BASKRETE initiative and the Laboratory for Transborder Cooperation“Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials” (LTC-Green Concrete). Economic support was providedby the Basque Government under the ELKARTEK Program [project NEOMAT (KK-2021/00059)]. In addition, Marta Diez-Garcia is grateful to the University of the Basque Country (UPV/EHU) and the University of Bordeaux for her pre-doctoral fellow-ship, within the framework of the Cross-Border Euroregional Campus of International Excellence IDEX Bordeaux–Euskampus. Francisco B. Aguirre acknowledges the funding received from Tecnalia to carry out his Ph.D. in cotutelle between the University of the Basque Country (UPV-EHU) and University of Bordeaux within the framework of the Cross-Border Euroregional Campus of International Excellence IDEX Bordeaux–Euskampus. Theauthors wish also to express their gratitude to the SAREN Re-search Group (IT-1619-22, Basque Government) and MCIN/AEI/10.13039/501100011033/ FEDER, UE (PID2021-124203OB-I00).

Stackings in graphene have a pivotal role in properties that could be useful in the future, as seen in the recently found superconductivity of twisted bilayer graphene. Beyond bilayer graphene, the stacking order of multilayer graphene can be rhombohedral, which shows flat bands near the Fermi level that are associated with interesting phenomena, such as tunable conducting surface states that can be expected to exhibit spontaneous quantum Hall effect, surface superconductivity, and even topological order. However, the difficulty in exploring rhombohedral graphenes is that in experiments, the alternating, hexagonal stacking is the most commonly found geometry and has been considered to be the most stable configuration for many years. Here we reexamine this stability issue in line with current ongoing studies in various laboratories. We conducted a detailed investigation of the relative stability of trilayer graphene stackings and showed how delicate this aspect is. These few-layer graphenes appear to have two basic stackings with similar energies. The rhombohedral and Bernal stackings are selected using not only compressions but anisotropic in-plane distortions. Furthermore, switching between stable stackings is more clearly induced by deformations such as shear and breaking of the symmetries between graphene sublattices, which can be accessed during selective synthesis approaches. We seek a guide on how to better control – by preserving and changing – the stackings in multilayer graphene samples., This research was funded by the Spanish Ministry of Science and Innovation (grants no. PID2019-105488GB-I00), the Gobierno Vasco UPV/EHU (project no. IT-1569-22), and the European Commission NRG-STORAGE project (project no. GA 870114) and H2020-FET OPEN Project MIRACLE (No. GA 964450). This research was conducted in the scope of the Transnational Common Laboratory (LTC) “Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials”.

This article belongs to the Special Issue Feature Papers in Construction and Building Materials., The use of nanomaterials to enhance the physical and mechanical properties and durability of cement materials in their hardened state has been studied for a long time in many investigations. In comparison, fewer studies focus on nanomaterials’ influence on the fresh state when the cement reaction starts. In addition, if we consider ternary blended cement (as those used for applications in marine environments), this has been rarely studied. Severe stresses in the marine environment require high durability, which is achieved by using pozzolanic additions, to the detriment of a rapid achievement of the properties. The addition of nanomaterials could contribute to increasing the durability and also accelerating the setting of the concrete. In this work, we performed a systematic and comparative study on the influence of adding graphene oxide (GO), nanosilica (NS), and microfibrillated cellulose (MFC) during the setting mechanisms of cement (CEM V/A suitable for concrete subjected to external attacks in marine environments) blended with fly ash and slag. Cement hardening was examined through setting time and rheology within mini-slump tests. The effect of nanoadditives on the cement hydration was analysed by heat flow calorimetry to evaluate the acceleration potential. Exploring the three nanoadditives on the same formulation, we could establish that the retention of mixing water significantly decreased workability for MFC. In contrast, NS increases the hydration of cement particles, acting as nucleation nodes and promoting supplementary cement hydrates (pozzolanic reactions) and accelerating setting time. Finally, GO showed a reduction in workability. We also investigated the dosage effects on mechanical behaviour at an early age and discovered an improvement even at low GO (0.006%) and NS (3%) dosages. We have also analysed the dosage effects on mechanical behaviour at an early age., This research was funded by the Euroregion Nouvelle Aquitaine-Euskadi-Navarre through DINaMO-FiVe research project and Grant No PID2019-104650GB-C21 (Agencia estatal de Investigacion, Spanish Government “Ministerio de Ciencia, Innovación y Universidades”).

Graphene is a two-dimensional material, with exceptional mechanical, electrical, and thermal properties. Graphene-based materials are, therefore, excellent candidates for use in nanocomposites. We investigated reduced graphene oxide (rGO), which is produced easily by oxidizing and exfoliating graphite in calcium silicate hydrate (CSHs) composites, for use in cementitious materials. The density functional theory was used to study the binding of moieties, on the rGO surface (e.g., hydroxyl-OH/rGO and epoxide/rGO groups), to CSH units, such as silicate tetrahedra, calcium ions, and OH groups. The simulations indicate complex interactions between OH/rGO and silicate tetrahedra, involving condensation reactions and selective repairing of the rGO lattice to reform pristine graphene. The condensation reactions even occurred in the presence of calcium ions and hydroxyl groups. In contrast, rGO/CSH interactions remained close to the initial structural models of the epoxy rGO surface. The simulations indicate that specific CSHs, containing rGO with different interfacial topologies, can be manufactured using coatings of either epoxide or hydroxyl groups. The results fill a knowledge gap, by establishing a connection between the chemical compositions of CSH units and rGO, and confirm that a wet chemical method can be used to produce pristine graphene by removing hydroxyl defects from rGO., This research was funded by Karlsruhe House of Young Science (KHYS), and Deutsche Forschungsgemeinschaft (DFG). A.A. and J.S.D. also acknowledge funding from the Spanish Ministry of Science and Innovation (grants nos. PID2019-105488GB-I00 and PCI2019-103657 grant), the Gobierno Vasco UPV/EHU (project no. IT-1246-19), and the European Commission NRG-STORAGE project (project no. GA 870114). Research conducted in the scope of the Transnational Common Laboratory (LTC) Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials.

The correlation between transport properties across subnanometric metallic gaps and the optical response of the system is a complex effect that is determined by the fine atomic-scale details of the junction structure. As experimental advances are progressively accessing transport and optical characterization of smaller nanojunctions, a clear connection between the structural, electronic, and optical properties in these nanocavities is needed. Using ab initio calculations, we present here a study of the simultaneous evolution of the structure and the optical response of a plasmonic junction as the particles forming the cavity, two Na380 clusters, approach and retract. Atomic reorganizations are responsible for a large hysteresis of the plasmonic response of the system, which shows a jump-to-contact instability during the approach process and the formation of an atom-sized neck across the junction during retraction. Our calculations demonstrate that, due to the quantization of the conductance in metal nanocontacts, atomic-scale reconfigurations play a crucial role in determining the optical response of the whole system. We observe abrupt changes in the intensities and spectral positions of the dominating plasmon resonances and find a one-to-one correspondence between these jumps and those of the quantized transport as the neck cross-section diminishes. These results reveal an important connection between transport and optics at the atomic scale, which is at the frontier of current optoelectronics and can drive new options in optical engineering of signals driven by the motion and manipulation of single atoms., We acknowledge financial support from Projects FIS2013-41184-P and MAT2013-46593-C6-2-P from MINECO. M.B., P.K., F.M., and D.S.P. also acknowledge support from the ANR-ORGAVOLT project and the Euroregion Aquitaine-Euskadi program. M.B. acknowledges support from the Departamento de Educacion of the Basque Government through a Ph.D. grant. P.K. acknowledges financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union. J.A. also acknowledges support from Grant 70NANB15H321, “PLASMOQUANTUM”, from the US Department of Commerce (NIST).

arXiv:1512.02104v2, We present a study of the optical response of compact and hollow icosahedral clusters containing up to 868 silver atoms by means of time-dependent density functional theory. We have studied the dependence on size and morphology of both the sharp plasmonic resonance at 3–4 eV (originated mainly from sp-electrons), and the less studied broader feature appearing in the 6–7 eV range (interband transitions). An analysis of the effect of structural relaxations, as well as the choice of exchange correlation functional (local density versus generalised gradient approximations) both in the ground state and optical response calculations is also presented. We have further analysed the role of the different atom layers (surface versus inner layers) and the different orbital symmetries on the absorption cross-section for energies up to 8 eV. We have also studied the dependence on the number of atom layers in hollow structures. Shells formed by a single layer of atoms show a pronounced red shift of the main plasmon resonances that, however, rapidly converge to those of the compact structures as the number of layers is increased. The methods used to obtain these results are also carefully discussed. Our methodology is based on the use of localised basis (atomic orbitals, and atom-centered and dominant-product functions), which bring several computational advantages related to their relatively small size and the sparsity of the resulting matrices. Furthermore, the use of basis sets of atomic orbitals also allows the possibility of extending some of the standard population analysis tools (e.g. Mulliken population analysis) to the realm of optical excitations. Some examples of these analyses are described in the present work., This work is supported, in part, by the ORGAVOLT (ORGAnic solar cell VOLTage by numerical computation) Grant ANR-12-MONU-0014-02 of the French Agence Nationale de la Recherche (ANR) 2012 Programme Modèles Numériques. F Marchesin, P Koval and D Sánchez-Portal acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) through the sfb1083 project, the Spanish mineco MAT2013-46593-C6-2-P project, the Euroregion Aquitaine-Euskadi program and from the Basque Departamento de Educación, upv/ehu (Grant No. IT-756-13). Peter Koval acknowledges financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union.

This article belongs to the Special Issue 50th Anniversary of the Kohn-Sham Theory—Advances in Density Functional Theory., Ionization potentials (IPs) and electron affinities (EAs) are important quantities input into most models for calculating the open-circuit voltage (Voc) of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB) method with the third-order self-consistent charge (SCC) correction and the 3ob parameter set (the third-order DFTB (DFTB3) organic and biochemistry parameter set) against experiments (for smaller molecules) and against first-principles GW (Green’s function, G, times the screened potential, W) calculations (for larger molecules of interest in organic electronics) for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT), but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field) SCC-DFTB calculations for first IPs (good to ± 0.649 eV). When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT) IPs) as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here) for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT) orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of interest to other researchers interested in DFTB investigation of large and complex problems, such as those encountered in organic electronics., This work is supported, in part, by the ORGAVOLT (ORGAnic solar cell VOLTage by numerical computation) Grant ANR-12-MONU-0014-02 of the French Agence Nationale de la Recherche (ANR) 2012 Programme Modèles Numériques. Mathias P. Ljungberg, Peter Koval and Daniel Sánchez-Portal acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) through the SFB (Sonderforschungsbereich) 1083 project, the Spanish MINECO (Ministerio de Economía y Competitividad) MAT2013-46593-C6-2-P project and the Euroregion Aquitaine-Euskadi program and support from the Basque Departamento de Educación, UPV/EHU (University of the Basque Country) (Grant No. IT-756-13). Peter Koval acknowledges financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union. Ala Aldin M. H. M. Darghouth would like to thank the French and Iraq governments for support through a Campus France scholarship. Walid Taouali would like to acknowledge support from the government of Tunisia.

Electromagnetic field localization in nanoantennas is one of the leitmotivs that drives the development of plasmonics. The near-fields in these plasmonic nanoantennas are commonly addressed theoretically within classical frameworks that neglect atomic-scale features. This approach is often appropriate since the irregularities produced at the atomic scale are typically hidden in far-field optical spectroscopies. However, a variety of physical and chemical processes rely on the fine distribution of the local fields at this ultraconfined scale. We use time-dependent density functional theory and perform atomistic quantum mechanical calculations of the optical response of plasmonic nanoparticles, and their dimers, characterized by the presence of crystallographic planes, facets, vertices, and steps. Using sodium clusters as an example, we show that the atomistic details of the nanoparticles morphologies determine the presence of subnanometric near-field hot spots that are further enhanced by the action of the underlying nanometric plasmonic fields. This situation is analogue to a self-similar nanoantenna cascade effect, scaled down to atomic dimensions, and it provides new insights into the limits of field enhancement and confinement, with important implications in the optical resolution of field-enhanced spectroscopies and microscopies., We acknowledge financial support from projects FIS2013-14481-P and MAT2013-46593-C6-2-P from MINECO. M.B., P.K., F.M., and D.S.P. also acknowledge support from the ANR-ORGAVOLT project and the Euroregion Aquitaine-Euskadi program. M.B. acknowledges support from the Departamento de Educacion of the Basque Government through a PhD grant, as well as from Euskampus and the DIPC at the initial stages of this work. R.E. and P.K. acknowledge financial support from the Fellows Gipuzkoa program of the Gipuzkoako Foru Aldundia through the FEDER funding scheme of the European Union, “Una manera de hacer Europa”.

Two self-consistent schemes involving Hedin's GW approximation are studied for a set of sixteen different atoms and small molecules. We compare results from the fully self-consistent GW approximation (SCGW) and the quasiparticle self-consistent GW approximation (QSGW) within the same numerical framework. Core and valence electrons are treated on an equal footing in all the steps of the calculation. We use basis sets of localized functions to handle the space dependence of quantities and spectral functions to deal with their frequency dependence. We compare SCGW and QSGW on a qualitative level by comparing the computed densities of states (DOS). To judge their relative merit on a quantitative level, we compare their vertical ionization potentials (IPs) with those obtained from coupled-cluster calculations CCSD(T). Our results are futher compared with >one-shot> G0W0 calculations starting from Hartree-Fock solutions (G0W0-HF). Both self-consistent GW approaches behave quite similarly. Averaging over all the studied molecules, both methods show only a small improvement (somewhat larger for SCGW) of the calculated IPs with respect to G0W0-HF results. Interestingly, SCGW and QSGW calculations tend to deviate in opposite directions with respect to CCSD(T) results. SCGW systematically underestimates the IPs, while QSGW tends to overestimate them. G0W0-HF produces results which are surprisingly close to QSGW calculations both for the DOS and for the numerical values of the IPs. © 2014 American Physical Society., P.K. acknowledges support from the CSIC JAE-doc program, co-financed by the European Science Foundation, and the Diputación Foral de Gipuzkoa. D.S.P. and P.K. acknowledge financial support from the Consejo Superior de Investigaciones Científicas (CSIC), the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02), the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa, and the German DFG through the SFB 1083. D.F. acknowledges support from the ORGAVOLTANR project and the Eurorégion Aquitaine-Euskadi program.

The spectroscopic properties of Nd3+ ions in Na3La9O3(BO3)8 single crystals have been studied, for the first time, by using steady-state and time-resolved laser spectroscopy. Site selective laser emission and excitation measurements have been performed to characterize the different sites for the rare-earth in this crystal. These results show the existence of at least two different sites for Nd3+ ions., This work was supported by the Aquitaine-Euskadi Program, Spanish Government MEC (MAT2004-03780), Basque Country University (UPV13525/2001) and the Conseil Régional d’Aquitaine (No. 9004120418171010).

The role of valence electrons in filling inner-shell vacancies of highly charged ions in metals is studied using self-consistent solid state screened potentials. Explicit results for Ne and N ions in Au and Al targets are presented and discussed in connection to recent experiments. These filling rates are fundamental in understanding the neutralization and relaxation of highly charged ions in solids., The authors gratefully acknowledge help and financial support by Fondo de Cooperacion Euskadi-Aquitania, Ministerio de Educacion y Ciencia, HCM program under Contract No. CHRX-CT93-0103, Euskal Herriko Unibertsitatea, Gipuzkoako Foru Aldundia, and Iberdrola S.A.

This article belongs to the Special Issue Nanostructured Materials for Energy Applications., Electrical conductive properties in cement-based materials have received attention in recent years due to their key role in many innovative application (i.e., energy harvesting, deicing systems, electromagnetic shielding, and self-health monitoring). In this work, we explore the use 3D printing as an alternative method for the preparation of electrical conductive concretes. With this aim, the conductive performance of cement composites with carbon nanofibers (0, 1, 2.5, and 4 wt%) was explored by means of a combination of thermogravimetric analysis (TGA) and dielectric spectroscopy (DS) and compared with that of specimens prepared with the traditional mold method. The combination of TGA and DS gave us a unique insight into the electrical conductive properties, measuring the specimens’ performance while monitoring the amount in water confined in the porous network. Experimental evidence of an additional contribution to the electrical conductivity due to sample preparation is provided. In particular, in this work, a strong correlation between water molecules in interconnected pores and the σ(ω) values is shown, originating, mainly, from the use of the 3D printing technique., This work was born under the umbrella of the ECRETE project (RTI2018-098554-B-I00) funded by MCIN/AEI/10.13039/501100011033 (Program I+D+i RETOS INVESTIGACIÓN 2018), the project PoroPCM (PCI2019-103657) funded by MCIN/AEI/10.13039/501100011033 and co-founded by the European Union (Programación Conjunta Internacional 2019) and the project NRG-STORAGE (GA 870114) funded by the European Commission. Research conducted in the scope of the Transnational Common Laboratory (LTC) Aquitaine-Euskadi Network in Green Concrete.