Ideal strength on clusters from first principles: the Ti13 case

The mechanical behavior of a Ti-13 cluster, based on total energy mechanical quantum calculations is studied. The cluster geometry has been optimized and good agreement with previous reports has been found. Axial strain is applied along one of the principal axes and the changes on the energetic and vibrational properties of the system are followed. To characterize the cluster stability as a function of strain, vibrational frequencies and total energy have been calculated, to obtain the cluster maximum load tolerance for compression (C) and tensile (T). If the maximum load is defined through a vibrational instability, it happens to be two and half, and three times larger than when the maximum total energy is considered (C and T respectively). As a result of the induced strain along of the C-5 symmetry element, the cluster changes its point group symmetry from I-h to D-5d, with an energy difference of 1.17 eV (for compression) and 0.33 eV (for tension) with respect to the ground state geometry. The electronic changes are also characterized, as function of the strain, by following the modifications of the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and changes on the total atomic population.