Theoretical investigation of corrosion inhibition by 5-hydrazino tetrazole tautomers using DFT calculations and Monte Carlo simulation

Copper, as a highly utilized metal, is continuously exposed to corrosion by various agents, including acids, bases and corrosive environments. The aim of the current study is to investigate the anticorrosive effect of different tautomers of 5-hydrazinotetrazole on three copper crystal surfaces, namely Cu (111), Cu (110), and Cu (100) using density functional theory (DFT) and Monte Carlo simulations (MC). Comparing the stability of the tautomers revealed that 5-hydrazino- 1H -tetrazole and 5-hydrazino- 2H -tetrazole structures are more stable than the other tautomeric forms. Therefore, the adsorption behavior of these two tautomers on copper surfaces was investigated in both perpendicular and parallel configurations. We applied DMol3 calculations to investigate quantum parameters, including the energy of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), global hardness (η), and electronegativity (χ) to evaluate the electronic properties of the inhibitors. The results indicated that the 2 H form is more stable than the 1 H form in the gas phase by 5.429 kcal/mol. However, analysis of the adsorption energies and other parameters such as the Fukui function and Mulliken charge revealed that the 1 H tautomer interacts more effectively with the Cu surface than the other isomeric form. Among the three copper surfaces, Cu (110) exhibited the most effective electronic interaction with the inhibitors. The highest adsorption was observed for the 1H tautomer in a perpendicular orientation via the N2 atom on the Cu (110) surface, with an adsorption energy of −53.056 kcal/mol and a Gibbs free energy of adsorption of −40.16 kcal/mol.