Structural Evolution of Tc<sub><i>n</i></sub> (<i>n</i> = 4–20) Clusters from First-Principles
Global Minimization
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Abstract
We
explore the structural evolution of Tc<sub><i>n</i></sub> (<i>n</i> = 4–20) clusters using a first-principles
global minimization technique, namely, basin-hopping from density
functional theory geometry optimization (BH-DFT). Significantly more
stable structures have been found in comparison with previous models,
indicating the power of DFT-based basin hopping in finding new structures
for clusters. The growth sequence and pattern for <i>n</i> from 4 to 20 are analyzed from the perspective of geometric shell
formation. The binding energy per atom, relative stability, and magnetic
moments are examined as a function of the cluster size. Several magic
sizes of higher stability and symmetry are discovered. In particular,
we find that Tc<sub>19</sub> prefers an O<sub>h</sub> symmetry structure,
resembling a piece of a face-centered-cubic metal, and its electrostatic
potential map shows interesting features that indicate special reactivity
of the corner atoms