|
Atomic clusters have proved to be appealing systems in the development of nanoscience. Clusters form a bridge between the physics of atoms/molecules and that of bulk systems, and they can behave as the latter or the former depending on the specific situation under study. Here, we report examples of the cases case where finite size effects either play an essential role or disappear: the lifetime of electronic excitations and the energy loss of external probes colliding with nano-sized targets.
First, we use density functional theory and the GW approximation to show the influence of confinement effects on the lifetime of electronic excitations. Two effects that depend on the cluster size are discussed: the change in the number of final states to which the excitation can decay, and the modification in the screened interaction between electrons. When compared to the case of solids, we show that the lifetime of electronic excitations in nanoclusters can be either longer or shorter depending on the excitation energy, thus leading to behaviour intrinsically different to the bulk case.
Secondly, we use time-dependent density functional theory to obtain the energy lost by atomic charged projectiles undergoing collisions with metal clusters of different sizes. It follows from our results that the effective energy loss per unit path length inside the cluster is nearly independent of cluster size over a wide range of projectile velocities. This allows us to associate this quantity to the stopping power in a bulk metal target. The calculated stopping power leads to a fair agreement with previous calculations for the bulk, as well as with recent experimental data. We thus set a new quantum-mechanical approach where accurate values for the stopping power of charges in solids can be obtained from ab initio calculations on finite-size systems.
|