Effect of hydrogen on ground state structures of small silicon clusters
Abstract
We present results for ground state structures of small Si_{n}H (2 \leq \emph{n} \leq 10) clusters using the Car-Parrinello molecular dynamics. In particular, we focus on how the addition of a hydrogen atom affects the ground state geometry, total energy and the first excited electronic level gap of an Si_{n} cluster. We discuss the nature of bonding of hydrogen in these clusters. We find that hydrogen bonds with two silicon atoms only in Si_{2}H, Si_{3}H and Si_{5}H clusters, while in other clusters (i.e. Si_{4}H, Si_{6}H, Si_{7}H, Si_{8}H, Si_{9}H and Si_{10}H) hydrogen is bonded to only one silicon atom. Also in the case of a compact and closed silicon cluster hydrogen bonds to the cluster from outside. We find that the first excited electronic level gap of Si_{n} and Si_{n}H fluctuates as a function of size and this may provide a first principles basis for the short-range potential fluctuations in hydrogenated amorphous silicon. Our results show that the addition of a single hydrogen can cause large changes in the electronic structure of a silicon cluster, though the geometry is not much affected. Our calculation of the lowest energy fragmentation products of Si_{n}H clusters shows that hydrogen is easily removed from Si_{n}H clusters.