  LEED experiments show that Li adsorbed at Cu(100) surfaces at room
temperature induces a (2x1) missing row substrate reconstruction while
adsorption at lower temperatures, T=180 K, results in an unreconstructed
Cu(100)+c(2x2)--Li overlayer structure. Substrate reconstruction has not been
observed for Na nor for K adsorption. In order to study the specific
reconstruction behavior of the Li adsorbate ab initio DFT calculations have
been performed on Cu(100)+Ad, Ad = Li, Na, K systems at coverages
Theta_Ad=0.25-0.5 with and without reconstruction. The calculations show that
the (2x1) MR reconstructed surface lies energetically above the ideal (1x1)
surface by 0.2 eV per unit cell. However, alkali binding is stronger in the MR
geometry as compared to that of the ideal surface where the increase in bond
strength becomes smaller in going from Li to Na to K. As a result, the MR
reconstructed and the overlayer adsorbate systems are energetically very close
for Cu(100)+Li while for Na and K the overlayer geometry is always favored.
