  Molecules in space are synthesized via a large variety of gas-phase
reactions, and reactions on dust-grain surfaces, where the surface acts as a
catalyst. Especially, saturated, hydrogen-rich molecules are formed through
surface chemistry. Astrochemical models have developed over the decades to
understand the molecular processes in the interstellar medium, taking into
account grain surface chemistry. However, essential input information for
gas-grain models, such as binding energies of molecules to the surface, have
been derived experimentally only for a handful of species, leaving hundreds of
species with highly uncertain estimates. Moreover, some fundamental processes
are not well enough constrained to implement these into the models.
  The proceedings gives three examples how computational chemistry techniques
can help answer fundamental questions regarding grain surface chemistry.
