A computational chemistry study on friction of h-MoS₂. Part I. Mechanism of single sheet lubrication

In this work, we theoretically investigated the friction mechanism of hexagonal MoS₂ (a well-known lamellar compound) using a computational chemistry method. First, we determined several parameters for molecular dynamics simulations via accurate quantum chemistry calculations and MoS ₂ and MoS_2-X O_xstructures were successfully reproduced. We also show that the simulated Raman spectrum and peak shift on X-ray diffraction patterns were in good agreement with those of experiment. The atomic interactions between MoS₂ sheets were studied by using a hybrid quantum chemical/classical molecular dynamics method. We found that the predominant: interaction between two sulfur layers in different MoS₂ sheets was Coulombic repulsion, which directly affects the MoS₂ lubrication. MoS₂ sheets adsorbed on a nascent: iron substrate reduced friction further due to much larger Coulombic repulsive interactions. Friction for the oxygen-containing MoS₂ sheets was influenced by not only the Coulomb repulsive interaction but also the atomic-scale roughness of the MoS₂/ MoS₂ sliding interface.