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 2.45Å 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 Na 3 , Na 4 , Na 5 , and the (2×2) Na overlayer. The binding is weak for Na 2 , which has a full valence electron shell. The presence of substrate modifies the structures of Na 3 , Na 4 , and Na 5 significantly, and both Na 4 and Na 5 are distorted from planarity. The calculated formation energies suggest that clustering of atoms is energetically favorable, and that the open shell clusters (e.g. Na 3 and Na 5 ) can be more abundant on graphite than in the gas phase. Analysis of the lateral charge density distributions of Na and Na 3 shows a charge transfer of ∼ 0.5 electrons in both cases.

Density functional study of alkali-metal atoms and monolayers on graphite (0001)

“…An exceptionally weak interaction of Na 2 with HOPG was found in our earlier study, 27 and further calculations of both horizontally and vertically aligned dimers show that the adsorption is also weak for the latter orientation (Table I). This indicates that Na 2 is almost decoupled from the surface, and the corresponding formation energy (∆E) is similar to that of a single adatom.…”

“…36 The model is similar to that used in our earlier work, 27 except that the supercell symmetry is hexagonal, not orthorhombic. This is a natural choice for graphite, and it enables us to use fewer k-points in the simulations.…”

First-principles calculations study of Na adsorbed on silicene

“…4a, the method, but the calculated energy barrier 0.25 eV is higher than 0.14 eV of NEB method (Supplementary Figure 1). However, even the smallest energy barrier 0.25 eV, is also far larger than the diffusion barrier 0.06 eV of Na diffusion on the graphite (0001) surface [29]. This observation implies that Na atom spreading on silicene sheet is not easy because of existence of buckling.…”

“…Since the hollow site is the most stable site of Na atom on perfect silicene, we chose its neighbor hollow site as the final site of diffusion process [29][30][31]. Meanwhile, four possible diffusion pathways a, b, c, and d, were designed in Fig.…”

Structures and energetics of lithium adatom and its dimer on graphene–a DFT study

“…It is generally accepted that the interaction between Li atoms and graphene presents an ionic character with a substantial charge transfer from the adsorbate to the carbon substrate [32][33][34][35]. Among all alkali-metals, Li has been identified as the most strongly binding atom [36]. While the detailed interaction mechanism is still controversial [37,38], in a recent study the adsorption of Li on narrow zigzag graphene nanoribbons (ZGNRs) has been studied extensively [39].…”