Making and breaking of chemical bonds under mechanical load

Peter Gumbsch

Brittle fracture as well as adhesion, or friction and wear are prominent examples for mechanical problems with clearly observable macroscopic consequences that are directly related to the processes of the formation and destruction of chemical bonds. Modelling such processes requires us to propagate the atomistic information through the scales to obtain macroscopic information. If chemical specificity and chemical accuracy are required, only few approaches are available.

I will quickly review latest achievements in concurrent coupling techniques, in particular the "earn on the fly" (LOTF) technique with applications to brittle fracture of diamond and silicon. The main focus of this talk will be the simulation of friction and wear processes between amorphous diamond-like carbon (DLC) films. Sequential techniques must be applied there to first obtain reasonable starting configurations for the atomic structure and topology of the films. Then different levels of approximations are required to assess the evolution of the friction contacts. Considerable attention must be paid there to extracting relevant information from large scale atomistic simulations, which in turn first requires an atomistic model for the hydrocarbons that can describe well the making and breaking of the atomic bonds. I will introduce such a new potential, report about comparison to large-scale tight binding simulations and present results for the evolution of an atomistically determined friction coefficient during running-in of such a contact.