ALKALI-METAL-ATOM CHEMISORPTION ONTO A METAL-SURFACE

Recent theoretical and experimental work implies that an alkali-metal atom chemisorbed onto a metal surface can be viewed within adressed-atom picture, i.e., as an atom whose wave functions are perturbed due to its interaction with the surrounding host lattice. This picture is similar to that used for a noble-gas atom physisorbed onto a metal surface. Such an approach utilizes the calculational method of the coupled Hartree-Fock theory, and it is applied in the present work to the chemisorption of a potassium atom onto a semi-infinite Na(001) substrate. Results for the Hartree-Fock ground state of the chemisorbed K atom, its induced dipole moment, and induced splitting of its p-orbital states are calculated at various substrate-adatom separations. It has been found that the induced dipole moment exhibits a maximum in its absolute value as the metal-adatom separation changes; most of the contribution to the dipole moment is due to the 3s- and 4s-electron states, while the pz states have been found to be counterpolarized, i.e., they polarize toward the vacuum side. On the other hand, the calculated dipole moments of the adatom were found to be too small to account for the observed work-function changes during alkali-metal chemisorption on a mteal surface. © 1990 The American Physical Society.