Abstract
A correlation study is addressed between quantum chemical parameters of five electronic states using Density Functional Theory (DFT) of Urea (U), Thiourea (TU), Selenourea (SU) and Guandine (GU) with the experimentally measured protection efficiency (%P) for the corrosion of low carbon steel in sulphuric acid medium. The best correlation is found for the ground electronic state (S-0) of SU followed by TU, U and GU. The results indicate that the chemical model based on bonding between inhibitor and metal is more consistent than the physical model based on electrostatic attraction between heteroatoms and metal.