Structure and stability of the N-hydroxyurea dimer: Post-Hartree-Fock quantum mechanical study

The potential energy surface (PES) search of the N-hydroxyurea dimer was se arched with second-order Moller-Plesset perturbation theory (MP2) and the 6 -31G(d,p) basis set. Eight local minimum energy structures have been found. Four of them have relatively strong (Delta E similar to-10 to -13 kcal/mol ) intermolecular interactions and the others are moderately strongly intera cting species (Delta E similar to-3 to -7 kcal/mol). Final estimation of in teraction energies was performed using the larger 6-311G(df,pd) and 6-311G( 2df,2pd) basis sets. The predicted interaction energies are Delta E=-14.26 kcal/mol and -3.43 kcal/mol for the strongest and the weakest interacting f orms of the studied complex, respectively, at the MP2/6-311G(2df,2pd)//MP2/ 6-31G(d,p) level of theory. The self-consistent field (SCF) interaction ene rgy decomposition indicates the important influence of the deformation term magnitude on Delta E(SCF). The calculated electron correlation contributio n to Delta E(MP2) depends on the geometry of the system and varies from -0. 5 to -5 kcal/mol. The estimated influence of water on the stability (free e nergy of hydration) of N-hydroxyurea dimers using the self-consistent isode nsity polarized continuum (SCI-PCM) model of solvation varies from similar to-11 kcal/mol to similar to-21 kcal/mol. The forms predicted to be more st rongly interacting species in gas phase are less influenced by hydration th an the more weakly interacting ones. (C) 2000 American Institute of Physics . [S0021-9606(00)30535-9].