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Volumen II - SAM

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Figure 2. Minimum energy 3I configuration (a), and mobile 4I for ED (b) and EAM (c).<br />

Regarding the static simulations, details on 1I have been given in [20]. The most important features are: i)<br />

for both models the easiest jump occurs to a nearest neighbor with reorientation of the dumbbell axis, and ii)<br />

only structures are relevant for ED, whereas structures appear for EAM by on-site rotation or<br />

translation from . The obtained E m values are 0.62 eV / 0.60 eV for EAM / ED.<br />

For the remaining clusters, visual inspection of the sequences turns out to be very cumbersome, thus<br />

complicating the analysis. This stems from the numerous detected saddles that amount to small SIA<br />

rearrangements or oscillations within the cluster, leading to no migration as a whole. Clearly, these effects<br />

are rooted in the rather independent behavior of individual SIAs mentioned earlier. A global approach,<br />

capable of revealing the most salient features, is needed. Thus, two basic techniques were employed; the<br />

chain of local minima and connecting saddles was partitioned in sub-chains according to the lowest energy<br />

structure, keeping only those whose end points were spatially separated in more than a certain threshold<br />

distance. For each sub-chain, the maximum energy saddle was determined, and then the least of all those<br />

values chosen as candidate for overall energy barrier. The latter assertion, however, must be confirmed by<br />

visual inspection, because the associated transition state need not correspond to RCM translation (though<br />

generally it does). A complementary approach consists in ordering all the saddles according to increasing<br />

energy and single out (some of) those connecting to the lowest energy structure, which is how the tables<br />

below have been constructed.<br />

Table 1. Migration mechanisms and barriers for the 2I cluster and both potentials<br />

EAM<br />

Transition E m (eV)<br />

ED<br />

Transition E m (eV)<br />

D1 → D3 0.42 D1 → D2* 0.39<br />

D1 → D2 0.52 D1 → D3 0.42<br />

D1 → D3* 0.53 D1 → D2 0.55<br />

D1 → D1* 0.60<br />

D1 → C1<br />

0.65<br />

Figure 3. Optimum jump mechanisms for the 2I cluster<br />

1380

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