Chemical response of thioaldehydes to compression between magnesium oxide surfaces: A first-principles molecular dynamics study

Abstract

First-principles molecular dynamics (FPMD) simulations are used to investigate the chemical response of thioaldehyde (MeCHS) to compression between (001) surfaces of magnesium oxide (MgO), with the external load reaching values as high as 20 GPa. The results demonstrate that the application of a load transforms the MeCHS molecules into oligomers through the formation of CS, SS, and CC bonds between MeCHS monomers and through proton transfer. The application of a load facilitates the reactions by decreasing the distance between the reacting molecules. The oligomers bonded to the MgO surface through the formation of CO and SO bonds, involving an oxygen atom in the surface. Proton transfer between the oligomers and the surface was also observed. No reactions were observed to take place between the oligomers and the magnesium atoms. The formation of bonds with the oxygen atoms in the surface led to an increase in the MgO distances within the surfaces, and thus a large disruption of the surface structure. The changes in structure were found to be reversible until 18 GPa, suggesting that the MeCHS oligomers may be effective at inhibiting wear by preventing direct surface-surface contacts without introducing new sources of irreversible changes in the surface structure for a certain range of loads (until 18 GPa). As a whole, the study describes in detail the chemical behavior of MeCHS in response to compression between MgO surfaces. This information could be applied to other molecules containing sulfinyl chemical groups and other metal oxides surfaces.