Hinged and chiral polydiacetylene carbon crystals

Structures and properties are calculated for hinged and chiral polydiacetylene carbon phases, which consist entirely of carbon chains found in organic polydiacetylenes. Diffraction and spectroscopic results are consistent with those for the controversial reported carbon phases of unknown structure, which might have accidentally formed by the reaction of acetylenic chains. Predicted properties include (1) a semiconductor-to-metal transition upon doping, (2) a soft deformation mode that results in negative linear and area compressibilities, negative Poisson ratios and expected shape-memory and ferroelastic behavior for the hinged phases, and (3) optical activity, second harmonic generation and torsional and transverse compressional piezoelectricity for the chiral phase.