We study the two lowest-energy isomers of the Ge(111)-(2 X 1) surface, by a
state-of-the-art first-principles calculation of their optical spectra, in
cluding the electron-hole interaction effectsl A comparison of our results
with the available experimental data suggests that, at difference with the
silicon case, the stablest isomer differs from the standard "buckled Pandey
chains" reconstruction. This conclusion is supported by accurate total-ene
rgy results.