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Checker Essay

1244 words - 5 pages

INTRODUCTION

Sulphur corrosion, is one of clearest examples of chemical problems, affecting seriously the electric industry. An interesting case of study, is the corrosion on electric transformers, where one of the most involved agents is the dibenzyl disulfide (DBDS)[1]. This is a compound, used extensively in the electric generation industry as additive in mineral oil, performing as exceptional antioxidant. However, undergoing discussion and while some authors argue that some organic compounds which compose the oil, promote the corrosive action, other ones describe the DBDS as potential corrosion agent, responsible for persistent poisoning effects over copper, and triggering continuous electric failures in power transformers [1-3]. The development of oil refining techniques, and the use of passivators, have diminished the effects, but the problem remains, reasons why are labeled as not efficient solutions. Under this context, the mechanisms involved in this chemical phenomenon are still unclear, being studied with notorious interest [4].
As is known, the corrosion process can be represented through the interaction between the sulfured species (such as DBDS), and copper surface. As has been reported in literature, to represent the surface through a small metal model, such as a cluster, is a practical advantage avoiding the excessive computational cost of modeling solid systems. In this line, many studies of interaction and adsorption using metal clusters have been described in literature [5-7]. In this context, Density Functional Theory (DFT), has shown to be a valuable tool to describe accurately a lot of molecular properties, emerged from chemical reactions up to adsorption processes, at low computational cost [8-12].
Given the above, in this work, we claim to clarify like a first approximation and through of DFT approach, the energetic and electronic effects that govern the reaction between DBDS and Cu surface, this last one, represented through Cu7 cluster and focusing especially the interaction Cu – S.

COMPUTATIONAL METHODS
Taking in count the large number of DFT methods (functional and basis sets), a huge literature list of assessment studies has been performed, especially over finite models and clusters. Been described with balanced performance to energetic and structural properties, functionals based on generalized gradient approximation (GGA) and their hybrid version (HGGA) have been employed, altogether pseudopotentials ECP’s and all- electron basis sets, as def- and def2- have demonstrated good assessments in transition metal clusters and organic molecules [13, 14].
Additionally to referenced studies, a previous evaluation was performed where electronic parameters were compared, considering S-S and S-C bond dissociation, at different theoretical levels with experimental data (Table I). This proceeding also was applied to Cu2 and Cu7, also including vertical quantities of electron affinity, ionization potentials, chemical...

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