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 $\sim 50\mathrm{GPa}$ with $a$-C:H containing 80% ${\mathrm{sp}}^3$ carbon atoms. The ${\mathrm{sp}}^2\to {\mathrm{sp}}^3$ 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.

• Received 9 November 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.2081