First-principles calculation of the effect of stress on the chemical activity of graphene

Graphene layers are stable, hard, and relatively inert. We study how tensile stress affects σ and π bonds and the resulting change in the chemical activity. Stress affects more strongly π bonds that can become chemically active and bind to adsorbed species more strongly. Upon stretch, single C bonds are activated in a geometry mixing 120° and 90°, an intermediate state between sp2 and sp3 bonding. We use ab initio density functional theory to study the adsorption of hydrogen on large clusters and two-dimensional periodic models for graphene. The influence of the exchange-correlation functional on the adsorption energy is discussed.