Density Functional Theory: Practical Application and Their Limitations in Corrosion Inhibition Research

Corrosion inhibitors reduce the corrosion rate of metallic materials through the interaction of the inhibitor molecules with the metal surface using one or more heteroatoms. While experimental methods report this interaction in terms of the overall corrosion rates and inhibition efficiency, an important gap exists in fully understanding the mechanism of such interactions at the atomic and molecular levels. Such information can readily be obtained from quantum chemical methods. Density functional theory (DFT) is a quantum chemical method which measures the electron density p(r) of the corrosion inhibitor as an index for interpreting its chemical characteristics and predicting its interaction with the corroding metal surface. In conceptual DFT, the corrosion analyst calculates certain reactivity parameters of the inhibitor molecule from its ground state electronic density. While these descriptors may sometimes provide good prediction of corrosion inhibition efficiency, they are also faced with several limitations. This chapter provides a brief introduction to DFT and its theoretical basis. A summary of the reactivity descriptors and description of relevant basis sets is also provided. Some applications of conceptual DFT to corrosion inhibition research are also reported. While the DFT method is outstanding for augmenting corrosion experiments, salient limitations are also highlighted.