Sodium atoms and clusters on graphite by density functional theory
Abstract
Sodium atoms and clusters (N⩽5) on graphite (0001) are studied using density functional theory, pseudopotentials and periodic boundary conditions. A single Na atom is observed to bind at a hollow site 2.45 Å above the surface with an adsorption energy of 0.51 eV. The small diffusion barrier of 0.06 eV indicates a flat potential energy surface. Increased Na coverage results in a weak adsorbate-substrate interaction, which is evident in the larger separation from the surface in the cases of Na3, Na4, Na5, and the (2×2) Na overlayer. The binding is weak for Na2, which has a full valence electron shell. The presence of substrate modifies the structures of Na3, Na4, and Na5 significantly, and both Na4 and Na5 are distorted from planarity. The calculated formation energies suggest that clustering of atoms is energetically favorable, and that the open shell clusters (e.g., Na3 and Na5) can be more abundant on graphite than in the gas phase. Analysis of the lateral charge density distributions of Na and Na3 shows a charge transfer of ∼0.5 electrons in both cases.
- Publication:
-
Physical Review B
- Pub Date:
- May 2004
- DOI:
- 10.1103/PhysRevB.69.205404
- arXiv:
- arXiv:physics/0401096
- Bibcode:
- 2004PhRvB..69t5404R
- Keywords:
-
- 68.43.Hn;
- 73.22.-f;
- 36.40.Cg;
- Structure of assemblies of adsorbates;
- Electronic structure of nanoscale materials: clusters nanoparticles nanotubes and nanocrystals;
- Electronic and magnetic properties of clusters;
- Atomic and Molecular Clusters;
- Chemical Physics
- E-Print:
- 20 pages, 6 figures