Copyright © 2013 by Modern Scientific Press Company, Florida, USA International Journal of Modern Chemistry, 2013, 4(1): 1-10 International Journal of Modern Chemistry Journal homepage: www.ModernScientificPress.com/Journals/IJMChem.aspx ISSN: 2165-0128 Florida, USA Article Quantum Chemical Studies of Corrosion Inhibition and Adsorption Potentials of Amoxicillin on Mild Steel in HCl Solution Abdulfatai A. Siaka 1, *, N. O. Eddy 2 , S. O. Idris 2 , L. Magaji 3 , Z. N. Garba 2 , I. S. Shabanda 1 1 Department of Pure and Applied Chemistry, Kebbi State University of Science and Technology, Aliero, Nigeria 2 Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria 3 Department of Pure and Industrial Chemistry, Bayero University, Kano, Nigeria * Author to whom correspondence should be addressed; E-Mail: fatsaadaby@gmail.com. Article history: Received 19 December 2012, Received in revised form 26 January 2013, Accepted 27 January 2013, Published 28 January 2013. Abstract: Inhibition and adsorption potentials of amoxicillin for the corrosion of mild steel in solutions of HCl have been investigated using quantum chemical approaches. The quantum chemical study was carried out using semi-empirical and density functional theory methods. The results obtained showed that various concentrations of the amoxicillin studied inhibited the corrosion of mild steel in solutions of HCl through the mechanism of physiosorption as confirmed by values of activation energy and free energy of adsorption (below 80 kJ/mol and –40 kJ/mol). Quantum chemical studies data reveal excellent correlations between quantum chemical parameters (MNDO, AM1, RM1 and PM3 Hamiltonians) and experimental inhibition efficiencies. This suggests that amoxicillin is a good corrosion inhibitor. Keywords: inhibitor; quantum chemistry; corrosion; physiosorption; amoxicillin; mild steel. 1. Introduction Corrosion is a primary means by which metals deteriorate and is therefore a major industrial problem. The degradation occurs when metals come in contact with moisture, acids, bases, salts,