First principles study of the structure and stability of carbynes

Possible structures for carbynes are investigated by a first principles study and their free energy as a function of temperature and pressure is examined. A possible model combining elements from previous models is proposed for carbyne structures. Simulations show that structures can be constructed which agree well with results previously proposed in characterization work. The free energy of carbynes is calculated within wide ranges of temperature and pressure (1000–4000 K and 0–18 GPa) for 12 different structures. Results indicate that it is higher than the free energy of graphite in the whole studied region. Therefore, it seems that carbon-only carbynes are meta-stable structures. Introducing additional elements to stabilize the carbyne structures is discussed. Our calculations confirm that a solid consisting of carbyne chains can be stabilized by 3 CH3 end groups.