Bonding behavior and thermal stability of C54Si6: a first-principles molecular dynamics study.

By using a self-consistent plane-waves density functional approach we study the bonding behavior and the thermal properties of C(54)Si(6) heterofullerenes. Calculations are carried out by employing a generalized gradient approximation. Our investigation improves upon previous findings on the same system obtained via the local density approximation approach. This is due to a much larger search in configurational space and the explicit account of temperature effects. Overall, isomers can be classified in two groups. In the first, nearest-neighboring Si atoms form a subnetwork, while in the second the Si atoms are farther apart on the cage. In addition to structural optimization, we carried out first-principles molecular dynamics for temperatures up to T=3000 K on a time interval of 12 ps. These simulations show that Si-Si bond variations with temperature are less important when all Si atoms are found on a hexagon. Therefore, this structural arrangement is the most likely to be observed experimentally. Analysis of charge topology reveals that the amount of charge on each atom depends on the number of heterogeneous bonds, due to a significant charge transfer from the Si to the neighboring C atoms.