Atomic structure and mechanical properties of carbyne

The atomic structure and mechanical properties of the carbyne (monatomic linear chains), containing from 2 to 21 carbon atoms, are theoretically investigated by ab-initio methods. We demonstrate the existence of a stable cumulene structure in the inner part of chains with the number of atoms N > or = 10. We present a general stress-strain diagram of chains until the moment when they break, which enables to determine their strength, elasticity, and fragility. These diagrams can be utilized to calibrate empirical potentials, especially for large deviations of the atoms from the equilibrium positions. For chains with N > or = 4, the relationship between the strength of the chain and the binding energy of the edge atom in the chain is established. The existence of scale-effect and "even-odd" effect for such properties as strength, elasticity, and fragility is observed. We demonstrate that the five-atom carbon chains show the maximum strength value.