  The electronic behavior of various solid metals (Al, Ni, Cu, Au, Ti, and W)
under ultrashort laser irradiation is investigated by means of density
functional theory. Successive stages of extreme nonequilibrium on picosecond
time scale impact the excited material properties in terms of optical coupling
and transport characteristics. As these are generally modelled based on the
free-electron classical theory, the free-electron number is a key parameter.
However, this parameter remains unclearly defined and dependencies on the
electronic temperature are not considered. Here, from first-principles
calculations, density of states are obtained with respect to electronic
temperatures varying from 10^-2 to 10^5 K within a cold lattice. Based on the
concept of localized or delocalized electronic states, temperature dependent
free-electron numbers are evaluated for a series of metals covering a large
range of electronic configurations. With the increase of the electronic
temperature we observe strong adjustments of the electronic structures of
transition metals. These are related to variations of electronic occupation in
localized d bands, via change in electronic screening and electron-ion
effective potential. The electronic temperature dependence of nonequilibrium
density of states has consequences on electronic chemical potentials,
free-electron numbers, electronic heat capacities, and electronic pressures.
Thus electronic thermodynamic properties are computed and discussed, serving as
a base to derive energetic and transport properties allowing the description of
excitation and relaxation phenomena caused by rapid laser action.
