DFT study of self-coupling reaction of CF_(2(ads)) coadsorbed on Cu(111) surface for forming CF2=CF_(2(g))

摘要

Total energy calculations based on the density functional theory (DFT) with ultrasoft pseudopotential. generalized gradient spin-polarized approximation and the partial structural constraint path minimization (PSCPM) method were carried out to establish the energetically more favorable reaction pathways for the self-coupling reaction of coadsorbed CF_(2(ads)) leading to the formation of CF_2=CF_(2(ads)) on the Cu(111) surface. In addition, the calculated electronic properties, namely partial density of states (PDOS), suggest that the initial breaking of the Cu(111)-CF_(2(ads)) bond associating with the electron delocalization on the Cu(111) surface and the electron transfer from Cu(111) to both units of CF_(2(ads)) are factors controlling the energy barrier for self-coupling reaction. Finally, the calculated energy barrier (0.310 eV) for the self-coupling reaction of CF_(2(ads)) coadsorbed on the Cu(111) surface in comparison with that (0.204 eV) for the single α-fluoride elimination of adsorbed CF_(3(ads)) on the Cu( 111) surface qualitatively manifests that the formation of CF_2 = CF_(2(g)) at 250 K is limited by the self-coupling reaction of coadsorbed CF_(2(ads)) instead of the single α-fluoride elimination of adsorbed CF_(3(ads)).