  Quantum fluid (or hydrodynamic) models provide an attractive alternative for
the modeling and simulation of the electron dynamics in nano-scale objects.
Compared to more standard approaches, such as density functional theory or
phase-space methods based on Wigner functions, fluid models require the
solution of a small number of equations in ordinary space, implying a lesser
computational cost. They are therefore well suited to study systems composed of
a very large number of particles, such as large metallic nano-objects. They can
be generalized to include the spin degrees of freedom, as well as
semirelativistic effects such as the spin-orbit coupling. Here, we review the
basic properties, advantages and limitations of quantum fluid models, and
provide some examples of their applications.
