MP2 and B3LYP calculations were performed on complexes of nitric acid with water using the 6-311++G(2d,p) basis set to determine optimized geometries and binding energies for HNO(3)(...)nH(2)O systems (n = 1-4). The structures for the global minima for n = 1-4 have homodromic rings formed by successive hydrogen bonds. The potential energy surface for the HNO(3)(...)nH(2)O clusters is quite shallow. The first stable ion-pair configuration is obtained for a HNO(3)(...)4H(2)O Complex. The ion pair, H3O+-NO3, is separated by the three H2O molecules forming an Eigen-ion (H9O4+) type structure. The transition states and activation barriers for n = 1-4 were also determined. The zero-point corrected transition-state barrier for the ion pair is only 0.5 kcal/mol. Larger HNO(3)(...)nH(2)O clusters (n up to 32) were also determined to be dominated by the ion-pair motif.