  Studies on the interactions between an alkali atom and an alkaline earth ion
at low energy are important in the field of cold chemistry. In this paper we,
extensively, study the structure, interactions, and dynamics of (MgCs)$^+$
molecular ion. We use an ab initio approach based on the formalism of
non-empirical pseudo-potential for Mg$^{2+}$ and Cs$^+$ cores, large Gaussian
basis sets and full valence configuration interaction. In this context, the
(MgCs)$^+$ cation is treated as an effective two-electron system. Potential
energy curves and their spectroscopic constants for the ground and the first 41
excited states of $^{1,3}\Sigma^+$, $^{1,3}\Pi$ and $^{1,3}\Delta$ symmetries
are determined. Furthermore, we identify the avoided crossings between the
electronic states of $^{1,3}\Sigma^+$ and $^{1,3}\Pi$ symmetries. These
crossings are related to the charge transfer process between the two ionic
limits Mg/Cs$^+$ and Mg$^+$/Cs. In addition, vibrational-level spacings, the
transition and permanent dipole moments are presented and analysed. Using the
produced potential energy data, the ground-state scattering wave functions and
elastic cross sections for a wide range of energies are performed. Furthermore,
we predict the formation of translationally and rotationally cold molecular ion
(MgCs) + in the ground state electronic potential energy by stimulated Raman
type process aided by ion-atom cold collision. In the low energy limit (< 1
mK), elastic scattering cross sections exhibit Wigner law threshold behaviour;
while in the high energy limit the cross sections as a function of energy E go
as E$^{-1/3}$. A qualitative discussion about the possibilities of forming the
cold (MgCs)$^+$ molecular ions by photoassociative spectroscopy is presented.
