MOLECULAR-ORBITAL STUDY OF LI AND LIOH ADSORBED ON A CU(001) SURFACE

Hartree-Fock and configuration-interaction calculations were performed for Cu4Li and Cu4LiOH clusters to investigate the mechanism of the in teraction of Li with the Cu(001) surface and of the formation of linea r LiOH compounds on Cu(001). The charge-transfer-type (2)E state is th e ground state for Cu4Li. The calculated Li-surface distance of 2.01 A ngstrom and vibrational frequency of 309 cm(-1) agree well with the ex perimental values. Cu4Li also shows a non-charge-transfer-type (3)A(2) state, which is energetically very close to the (2)E state. The adsor ption energy (E(ad)) was calclated to be 2.32 eV for Cu4Li ((2)E). Con sideration of the 3d-correlation effect is indispensable for calculati ng E(ad) Cu4LiOH shows a stable state in which a linear LiOH is weakly bound to Cu-4 The vibrational frequency of Li normal to the surface d ecreases from 309 cm(-1) (Cu4Li) to 85 cm(-1) (Cu4LiOH). The present c alculations support the experimental finding by Tochihara and co-worke rs that a linear LiOH is formed on the surface when H2O interacts with the Li adatom on Cu(001) at low coverage. We also performed calculati ons for a larger Cu13Li cluster, and the results were similar to those using the small cluster of Cu4Li.