Anisotropic a-C:H from compression of polyacetylene.

Abstract

We have simulated the transformation of crystalline trans-polyacetylene into $a$-C:H under pressure by constant pressure ab initio molecular dynamics. Polyacetylene undergoes a gradual saturation of C-C bonds via chain interlinks, ending up at $\ensuremath{\sim}50\mathrm{GPa}$ with $a$-C:H containing 80% ${\mathrm{sp}}^{3}$ carbon atoms. The ${\mathrm{sp}}^{2}\ensuremath{\rightarrow}{\mathrm{sp}}^{3}$ conversion is irreversible and does not reverse by returning to zero pressure. The final $a$-C:H is a wide gap insulator and, at variance with the conventionally generated $a$-C:H, is highly anisotropic keeping some memory of the original polyacetylene chain axis.