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, A ll the functionals indicate that the (2)A' electronic state of a C-s v inylic structure corresponds to the absolute energy minimum, whereas t he (2)A(2) electronic state of the symmetric C-2v structure correspond s to a low-lying transition state governing the exchange of carbon ato ms. The inclusion of gradient corrections and basis set superposition error brings the computed binding energy into reasonable agreement wit h experiment. The computed hyperfine coupling constants are in good ag reement with experiment only for the C-2v structure. Taking into accou nt the low energy difference and the strongly different dipole moments of C-s and C-2v structures, it is possible that matrix trapping alter s the relative stabilities of different structures.