  We report on the formation of the high-energy empty-state resonance in the
electronic spectrum of the iron adatom on the Pt(111) surface. By using the
combination of the first-principles methods and the finite-temperature exact
diagonalization approach, we show that the resonance is the result of the
valence fluctuations between atomic configurations of the impurity. Our
theoretical finding is fully confirmed by the results of the scanning tunneling
microscopy measurements [M.F. Crommie et al., Phys. Rev. B 48, 2851 (1993)]. In
contrast to the previous theoretical results obtained by using local spin
density approximation, the paramagnetic state of the impurity in the experiment
is naturally reproduced within our approach. This opens a new way for
interpretation of STM data collected earlier for metallic surface nanosystems
with iron impurities.
