Black phosphorus exhibits a high degree of band anisotropy. However, we found
that its in-plane static screening remains relatively isotropic for momenta
relevant to elastic long-range scattering processes. On the other hand, the
collective electronic excitations in the system exhibit a strong anisotropy.
Band non-parabolicity leads to a plasmon frequency which scales as nβ,
where n is the carrier concentration, and β<21. Screening and
charge distribution in the out-of-plane direction are also studied using a
non-linear Thomas-Fermi model