  Electrostatic Gravitational or Rayleigh-Taylor (RT) instability in an
inhomogeneous magnetized multi-ions plasma with some fraction of quantum
mechanical electrons. The effect of Bohm potential, temperature degeneracy and
magnetic field are carried out. A generalized dispersion relation is deduced
under the drift approximation. The presence of negative ions with their
different streaming velocities make the dispersion relation a cubic equation.
Different roots of both real and imaginary parts of the RT mode are studied by
using the Cardano method of solving the cubic equation. The growth rates of RT
instability are examined analytically and numerically. It is shown that the
basic features of these waves are significantly modified by the positive and
negative ions drift speed as well as by the magnetic field and density.
Relevance of the work regarding to dense astrophysical plasmas is pointed out.
