Structural evolution and properties of subnanometer Tc_n (n = 2–15) clusters

All-electron scalar relativistic calculations of the geometric and electronic structures of neutral subnanometer Tc_n (n = 2–15) clusters have been performed using spin-polarized density functional theory. It is shown that the structural evolution of Tc_n clusters from n = 3 to n = 8 is similar to Mn clusters, which also belong to the group of VIIB transition metals. The calculated binding energy per atom varies gradually from 0.65 eV for Tc₂ to 2.35 eV for Tc₁₅. The computed electron affinity and ionization potential follow the classical electrostatic metallic droplet model for clusters larger than Tc₆ and converge asymptotically to the experimental value of the bulk Tc work function. A study of the kinetic stability of Tc clusters in terms of the second difference of binding energies and the energy gap between the frontier orbital states predicts Tc₃(D_3h), Tc₄(T_d), Tc₆(O_h), Tc₁₂(I_h), and Tc₁₃(I_h) to be the most stable clusters. Vibrational spectra of Tc clusters are also provided for further experimental identification.