Mechanism of enhanced broadening of the ionization level of Li outside transition metal surfaces

We show that the $d$-band of a transition metal surface induces intra-atomic hybridization of an atom in its vicinity. It is demonstrated that such hybridization can have a profound influence on the resonance width and hence lifetime of the atomic ionization level. The degree of Li $s\text{−}p$ hybridization is found to be directly correlated to the overlap of the $d$-band density of states with the Li $2s$ and $2p$ levels, and is shown to be not due solely to long-range electrostatic image potential effects.

Figure 1

PDOS for Li $2s$ (top) and Li $2p$ (bottom) for a Li atom $10\mathrm{a.u.}$ above a top site on the Ir(001) surface. $0\mathrm{eV}$ and $2.1\mathrm{eV}$ correspond to the $2s$ and $2p$ energy levels, respectively, of an isolated Li atom. Li $s\text{−}p$ mixing is observed.

Figure 2

Fraction of Li $2p$ PDOS [${\lambda }_{2p}$ in Eq. (3)] as a function of $d$-band proximity to the isolated Li $2s$ level. ${\lambda }_{2p}$ is calculated for Li $10\mathrm{a.u.}$ from each metal surface. Open $d$-shell transition metals exhibit the largest mixing of the Li energy level widths. The horizontal shaded area corresponds to the range of ${\lambda }_{2p}$ predicted from a jellium model that includes the image potential.

Figure 3

(Color online) Density difference plots for a Li atom $10\mathrm{a.u.}$ above top sites on four metal surfaces (Ir(001), Cu(001), Al(001), and Mg(0001)). These absolute differences represent up to $\sim 7.5\%$ changes in density, even at $10\mathrm{a.u.}$ away from the surface. Greatest polarization of the Li $2s$ occurs above transition metal surfaces and the polarization around the transition metal atoms occurs in patterns characteristic of $d$-orbitals.

Figure 4

Metal surface $d$-band DOS for a Li atom $10\mathrm{a.u.}$ above top sites on (a) Cu(001) and (b) Ir(001) surfaces. Vertical lines at 0 and $\sim 2.1\mathrm{eV}$ represent the positions of the isolated Li $2s$ and $2p$ levels, respectively. Larger overlap of the $d$ band with the Li $2s$ and $2p$ levels correlates with larger mixing.

Figure 5

Broadening of the ionization level of Li as a function of distance from Cu(001) and Al(001), including or neglecting Li $2s\text{−}2p$ mixing [Eq. (3)]. Although the Li energy level widths for Li near Al(001) are only slightly affected by Li $2s\text{−}2p$ mixing, the Li widths for Li near Cu(001) are significantly enhanced by accounting for the mixing.