  A recently developed model to describe proton collisions from molecules
involving basic atoms such as hydrogen, carbon, nitrogen, oxygen and phosphorus
(H, C, N, O, P) is extended to treat collisions with multiply charged ions. The
ion-atom collisions are computed using the two-center basis generator method
(TC-BGM), which has a proven track record of yielding accurate total cross
sections for electron capture and ionization. The atomic net ionization cross
sections are then used to assemble two models for ion-molecule collisions: an
independent atom model (IAM) that follows the Bragg additivity rule (labeled
IAM-AR), and also the so-called pixel-counting method (IAM-PCM). The latter
yields reduced cross sections relative to IAM-AR near the maximum, since it
takes into account the overlapping nature of effective cross sectional areas.
The IAM-PCM for higher-charge projectiles leads to strong reductions of net
ionization cross sections relative to the IAM-AR method, and is computed
directly for projectile charges $Q=1, 2, 3$. The scaling behavior of the
IAM-PCM is investigated over a wide range of energies $E$, and at high $E$ it
converges towards the IAM-AR. An empirical scaling rule is established which
allows to reproduce these results based on proton impact calculations. Detailed
comparisons are provided for the uracil target ($\rm C_4 H_4 N_2 O_2$), for
which other theoretical as well as experimental results are available. Based on
the scaling model derived from the IAM-PCM data it is shown how the
experimental data for uracil and water bombarded by multiply charged ions can
be reduced to effective $Q=1$ cross sections respectively, and these are
compared to proton impact data.
