Exact ground state of the generalized three-dimensional   Shastry-Sutherland model
  We generalize the Shastry-Sutherland model to three dimensions. By representing the model as a sum of the semidefinite positive projection operators, we exactly prove that the model has exact dimer ground state. Several schemes for constructing the three-dimensional Shastry-Sutherland model are proposed. 
Shu Chen and H. B\"uttner