*Quantum Chemical Methods as Efficient Tools to Study Corrosion Inhibitors*

Quantum chemical methods are seen to be very effective in determining the molecular structures as well as explaining the electronic structures and reactivity's of molecules. Computational chemistry is considerably used to assess the efficiency of corrosion inhibitors, this method helps to search compounds of desired property employing computational modelling. Quantum chemical method and molecular modelling techniques help in defining a large number of molecular parameters illustrating

the reactivity, shape, and binding properties of complete molecules as well as of individual molecular fragments and substituents. The prominent quantum chemical parameters are atomic charges, molecular orbital energies (*E*HOMO, *E*LUMO and Δ*E*gap), dipole moment, charge distribution. Density functional theory has successfully been applied to explain the importance of structure of corrosion inhibitors and their adsorption efficiency on the metal surfaces, however the properties of corrosion inhibitors like *E*HOMO, *E*LOMO, Δ*E*gap, dipole moment (μ), electronegativity ( Щ ), and atomic charge have by far achieved the appropriate correlation with corrosion inhibition efficiency.

#### **5. Emerging Embedment Methods of Corrosion Inhibitors**

Corrosion inhibitors can be incorporated into the coating formulation through different ways. One of the most commonly used methods is the direct addition of inhibitors in the primer or topcoat. However, a too high concentration or low solubility of the inhibitors often results in a deterioration of the integrity and physical barrier properties of the matrix of the protection system [101]. In addition, the existing interaction of the inhibiting agents with the protective matrix often leads to significantly reduced stability of the protective layer and the deactivation of the inhibitors. Recently, different new methods for inhibitor incorporation have emerged to prevent the direct interaction of inhibitor with the matrix. One of the most common methods is application of inhibitor loaded coatings. Coatings based on inhibitor loaded containers protect the metal by releasing corrosion inhibitor in response to changes in the coating integrity (cracks) or local environment (pH shift) caused by corrosion attack. These systems have been extensively investigated, because they are potential replacements for the banned chromate-based coatings [102]. Out of these, self-healing coating is an emerging and broad field to replace the chromate for corrosion control and autonomic repair of coatings (self-healing), which is discussed in this section.
