Structure and EPR parameters of CuC2H2 from a density functional approach

The structure, binding energy and harmonic force field of CuC2H2 have been studied using local and gradient-corrected density functionals. All the functionals indicate that the 2A′ electronic state of a Cs vinylic structure corresponds to the absolute energy minimum, whereas the 2A2 electronic state of the symmetric C2v structure corresponds to a low-lying transition state governing the exchange of carbon atoms. The inclusion of gradient corrections and basis set superposition error brings the computed binding energy into reasonable agreement with experiment. The computed hyperfine coupling constants are in good agreement with experiment only for the C2v structure. Taking into account the low energy difference and the strongly different dipole moments of Cs and C2v structures, it is possible that matrix trapping alters the relative stabilities of different structures.