A density functional study of phosphorus-doped clusters C_nP ₃⁺ (n=1-8)

We have designed numerous models of C_nP₃⁺ (n=1-8) using molecular graphics software. The geometry optimization and calculation of vibrational frequency were carried out by the B3LYP density functional method. The ground-state structures are straight carbon chains with a P₂C ring connected at one end and a phosphorus atom at the other. The bond length features of the straight chains suggest a polyacetylene-like structure for even n and cumulenic-like structure for odd n. The C _nP₃⁺ (n=1-8) with even number of carbon atoms are more stable than those with odd number. The odd/even alternation trend can be explained according to the variation of bonding characters, ionization potentials, and incremental binding energies.