  We present an explicit water molecular dynamics simulation of dilute
solutions of model alkyltrimethylammonium surfactant ions (number of methylene
groups in the tail is 3, 5, 8, 10, and 12) in mixture with NaF, NaCl, NaBr, and
NaI salts, respectively. The SPC/E model is used to describe water molecules.
Results of the simulation at 298 K are presented in the form of radial
distribution functions between nitrogen and carbon atoms of CH$_2$ groups on
the alkyltrimethylammonium ion, and the counterion species in the solution. The
running coordination numbers between carbon atoms of surfactants and
counterions are also calculated. We show that I$^-$ counterion exhibits the
highest, and F$^-$ the lowest affinity to "bind" to the model surfactants. The
results are discussed in view of the available experimental and simulation data
for this and similar solutions.
