QUANTUM CHEMICAL AND MONTE CARLO SIMULATIONS ON CORROSION INHIBITION EFFICIENCY OF 2-MERCAPTO-5-PHENYLFURAN AND BIS(PYRIDYL)OXADIAZOLES

A theoretical parameters for furan (inhibitor A), 3,5-bis(4-pyridyl)-1,2,4-oxidiazole (in-hibitor B) and 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (inhibitor C) were investigated using density functional theory (DFT) and Monte Carlo techniques at 6-311++G(d, p) basis set for protonated and non-protonated species in gas and aqueous phases. Quantum chemical calculations were done on three heterocyclic compounds which used as mild steel corrosion inhibitors in acid en-vironments to examine the link between inhibitor molecular structure and inhibition perfor-mance. Energy and distribution of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), charge distribution of the studied inhibitors, global soft-ness (o) and hardness (& eta;), energy back-donation (AEback-donation), electrophilicity and nucleophilic-ity, absolute electronegativity (y) values, bandgap energy (AEg), ionization potential, chemical potential and the fraction of electrons (ANmax) transfer from inhibitors to mild steel were also calculated and correlated with inhibition efficiencies. The results indicated that the inhibition efficacy of inhibitors improved with increasing HOMO energy and decreasing energy gap of frontier molecular orbital. By contributing electrons to mild steel, regions with N and O atoms are most likely to bond to the surface. DFT and Monte Carlo calculations were used to rank the three materials for anti-corrosion, and the experimental and theoretical results were very similar.