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Highlights • In the absence of pentagonal figures, new ones form, close to concave four-membered edges. • Addition of sulfur atoms is ruled by pentagonal figures in the vacant graphene system. • Electronic structure and magnetism are strongly affected by cancellation of dangling bonds. • The inclusion of one and two sulfur atoms is favorable. Abstract The conformational, magnetic and electronic study of one and two sulfur atoms doping on multivacancy graphene systems, using first principles calculations is presented. The location for the addition of the sulfur atoms is ruled by the presence of pentagonal figures in the optimized multivacancy graphene system or, in case of the absence of such figures, by the concave four membered structures in the vacancy. The electronic structure and the magnetism in these systems are strongly affected by the cancellation of dangling bonds due to the inclusion of sulfur atoms. Finally, it was possible to demonstrate that the inclusion of one and even a second sulfur atoms in the multivacancy graphene systems is favorable. [ABSTRACT FROM AUTHOR]

Abstract: The occurrence of ripples in an eight‐atom vacancy graphene system was analyzed through first principles calculations based on density functional theory. The study focuses on the conditions that should be considered in order that ripples could occur in the single layer defected graphene. The vacancies concentration, especially the pentagonal figures formed after relaxation of the vacant system, and the distances between neighbor pentagons, are found to be key aspects for rippling occurrence, with no charge distribution consequence. Two different configurations of rippling have been found where the position of the pentagonal figures is discussed as the driving force for any of them to occur. [ABSTRACT FROM AUTHOR]

The interaction between a complex porphyrin-like system formed by an iron atom and multivacant graphene layer and O 2 , CO and CO 2 molecules is studied, using Density Functional Theory (DFT) calculations. The multivacancy graphene system used for this study, consists in the removal of a 1,4-dimethybenzene-like moiety, in a 6 × 6 supercell. This removal and the structural optimization subsequently performed, yield to a biaxial vacancy, where the location of an iron atom embedded in it, lead to a system with resemblance to iron-porphyrin systems. This similar structure could be used to form complexes where gas molecules are allowed to interact with these iron-octavacant graphene systems. The study focuses on the structure of the system and the net magnetic moment for different gas molecules: O 2 , CO 2 and CO. Rippling in the vacant graphene is enhanced through this interaction. [ABSTRACT FROM AUTHOR]

Ab-initio calculations based on density functional theory (DFT) have been performed to study systems where a first row transition metal atom is embedded in a rippled graphene due to the existence of an 8-order multivacancy. In addition to these cases, also the inclusion of a zinc atom, with a 3d 10 electron configuration, was also studied. Structural distortions and magnetic response for each system were studied. A correlation was found for the magnitude of the rippling and the distortion in the vacancy. Variation in the trends was found for Cu and Zn cases, which were explained on the basis of the filling of the 3d x 2 -y 2 orbital. All the systems exhibit lower magnetic moment in comparison to the metal-less system. The quenching of the magnetic moment due to the carbon atoms in the vacancy is observed for Sc and Cu. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism. [ABSTRACT FROM AUTHOR]

This manuscript reports a comprehensive study of the stability and magnetism in graphene multivacancy systems, using Density Functional Theory (DFT) calculations, by means of the concept of the complementary figure, i.e. the sequence of carbon atoms removed to produce these defected graphene structures. We studied the role of the relative positions of the pentagonal rings that form after optimization in the resulting defected graphene structure, the occurrence of dangling bonds, their steric hindrance and the magnetic arrangements formed. The results here reported give an interesting approach to understand complex multivacancy graphene systems and contribute to this field by going further in the use of the complementary figure to characterize and predict the properties of such systems. [ABSTRACT FROM AUTHOR]

Abstract: The presence of Stone–Wales, single and double vacancy defect sites in bilayer graphene was studied by means of dispersion corrected density functional theory. Based on the analysis of the formation energies computed for monolayer and bilayer graphene, monovacancies are expected to be equally frequent in both materials. In the case of the single vacancy, the formation energy is barely affected by the second layer and so does the interlayer interaction energy. However, Stone–Wales and double vacancies may be expected to be more frequent in single layer graphene because their formation energies are expected to be lower as compared to bilayer graphene. Calculations employing very large unit cells would be interesting to reduce the effect of the incommensurability of the unit cells of perfect and defective graphene, and thus confirm the latter statement. The single and double vacancies have the similar formation energy in bilayer graphene but for monolayer graphene, the 5-8-5 divacancy is more stable by at least 0.7eV, in contrast with recent results. The electronic properties of defective bilayer graphene are similar to those corresponding to monolayer graphene. Finally, we have shown that the magnetic moment of monolayer graphene with a monovacancy is smaller than that of bilayer graphene bearing the same defect, when the unit cell is optimized. Yet, if the unit cells are fixed, different outcomes can be obtained. If the unit cell of perfect graphene is employed the magnetic moment of bilayer graphene with a single vacancy is larger, but if the unit cell of monolayer graphene with a single vacancy is to be employed the magnetic moment of defective bilayer graphene becomes smaller than that of monolayer graphene with a monovacancy. [Copyright &y& Elsevier]

Highlights • Optical and geometric features of multivacancy GQDs were studied using DFT calculations. • Square and pentagonal figures are important in the properties of such materials. • The configuration of the multivacancy is key for the geometric structure. • The differences between vacancies in graphene are likely to be related to non-periodicity. Abstract The optical properties and the geometric characteristics of multivacancy graphene quantum dots systems are studied using Density Functional Theory calculations, in a systematic way, in relation to the number of carbon atoms extracted and the relative configurations that could be present in the cluster. The way to characterize these configurations was using the complementary figure model -i.e. the figure formed by the carbon atoms extracted in order that the vacancy could be created-. The number of pentagonal or square figures formed after structure optimization, as well as their relative location, is found to be very relevant to determine the curvature level of the graphene quantum dot, but the occurrence of higher order cycles have a non-negligible role and cannot be ruled out. However, this occurrence is much dependent on the specific multivacancy to be studied and prevents to reach more accurate models that could allow the prediction of the magnitude of the curvature. We found unexpected instability in dendritic-like vacancies and we suggest that the non-periodic character of the graphene quantum dot, in contrast to graphene, would prevent such vacancies to be relaxed in a higher extension, causing this kind of systems to be less stable than, for example, zigzag complementary figures systems. [ABSTRACT FROM AUTHOR]

We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH 2 complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without H H bond are the preferential PtH 2 systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H 2 molecule is oriented almost perpendicular to the outermost C Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies. [ABSTRACT FROM AUTHOR]