  We investigate the possibility of producing ultracold NH3 molecules by
sympathetic cooling in a bath of ultracold atoms. We consider the interactions
of NH3 with alkali-metal and alkaline-earth atoms, and with Xe, using ab initio
coupled-cluster calculations. For Rb-NH3 and Xe-NH3 we develop full potential
energy surfaces, while for the other systems we characterize the stationary
points (global and local minima and saddle points). We also calculate isotropic
and anisotropic Van der Waals C6 coefficients for all the systems. The
potential energy surfaces for interaction of NH3 with alkali-metal and
alkaline-earth atoms all show deep potential wells and strong anisotropies. The
well depths vary from 887 1/cm for Mg-NH3 to 5104 1/cm for Li-NH3. This
suggests that all these systems will exhibit strong inelasticity whenever
inelastic collisions are energetically allowed and that sympathetic cooling
will work only when both the atoms and the molecules are already in their
lowest internal states. Xe-NH3 is more weakly bound and less anisotropic.
