Carbon string structures: First-principles calculations of quantum conductance

Carbon forms various nanostructures based on the monatomic chains or strings which show transport properties of fundamental and technological interest. We have carried out first-principles quantum conductance calculations using optimized structures within density functional theory. We treated finite segments of carbon monatomic chain, metal-semiconductor heterostructure, and resonant tunneling double barrier formed of C-BN chains, as well as symmetric and antisymmetric loop devices between two electrodes. We examined the effects of electrode, contact geometry, size of the device, strain, and foreign atoms adsorbed on the chain. Calculated quantum ballistic conductance of carbon chains showing even-odd disparity depending on the number of atoms and strain are of particular interest. Notably, chains consisting of an even number of carbon atoms contacted to metal electrodes display a resonant tunneling-like behavior under axial strain. The double covalent bonding of carbon atoms depicted through self-consistent charge density analysis underlies unusual transport properties.