  We analyse the evolution of scalar field dark energy in the spherical halos
of dark matter at the late stages of formation of gravitationally bound systems
in the expanding Universe. The dynamics of quintessential dark energy at the
center of dark matter halo strongly depends on the value of effective sound
speed $c_s$ (in units of speed of light). If $c_s\sim1$ (classical scalar
field) then the dark energy in the gravitationally bound systems is only
slightly perturbed and its density is practically the same as in cosmological
background. The dark energy with small value of sound speed ($c_s<0.1$), on the
contrary, is important dynamical component of halo at all stages of their
evolution: linear, non-linear, turnaround, collapse, virialization and later up
to current epoch. These properties of dark energy can be used for constraining
the value of effective sound speed $c_s$ by comparison the theoretical
predictions with observational data related to the large scale gravitationally
bound systems.
