From structure to surface tension of small silicon clusters by Quantum Monte Carlo simulations

We investigate the structural, surface and electronic properties of small silicon clusters Si n (for n = 2 to 15) using HF, DFT and FN-DMC calculations. We analyze the atomic configurations, surface properties and electronic structures and show that the radius and average surface area of the clusters can be modeled by a Jellium-type model. We found that the surface tension sigma of the clusters decreases with increasing cluster size in the range of the clusters under investigation. An estimate of the surface tension for bulk silicon yields sigma bwk = 0 . 88(3) J/m 2 in agreement with recent experiments. The average bond length of the clusters shows a non-monotonic behavior. Smaller clusters exhibit a high spin state influenced by electron correlation, especially during the 2D to 3D structural transition, which occurs at n = 4 to n = 5. We also find that the Si 4 , Si 10 and Si 12 clusters exhibit enhanced stability due to electron correlation. Our results are consistent with the experiments on bond length, binding energy and dissociation energy.