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Density functional theory was used at the B3LYP/6-311++G(d,p) level of theory to study the hydrates of 2NH3:H2SO4:nH2O for n = 0～4. Neutrals of the most stable clusters, when n = 0 and 1, spontaneously formed and were determined to be hydrogen-bonded molecular complexes of monomeric species. Double ions (clusters containing a NH4+ cation and a HSO4- anion) or even ternary ions (clusters with two NH4+ cations and one SO42- anion) spontaneously formed in the most stable clusters of 2NH3:H2SO4:nH2O (n = 2, 3, 4). The energetics of binding and incremental association was also calculated. Double ions are not energetically favorable until 2NH3:H2SO4:2H2O because of the about equal free energies for forming the neutral (the most stable) and double ion (the second stable) isomers. The free energy of incremental association from free H2O and 2NH3:H2SO4:nH2O has a maximum at n = 2 at room temperature with ΔG ≈ -2 kcal/mol. The comparison of incremental association energies between 2NH3:H2SO4:nH2O, NH3:H2SO4:nH2O and H2SO4:nH2O clusters revealed that NH3 plays an important role in the atmospheric particle nucleation.
Density functional theory was used at the B3LYP / 6-311 ++ G (d, p) level of theory to study the hydrates of 2NH3: H2SO4: nH2O for n = 0-4. Neutrals of the most stable clusters, when n = 0 and 1, spontaneously formed and were determined to hydrogen-bonded molecular complexes of monomeric species. Double ions (clusters containing a NH4 + cation and a HSO4- anion) or even ternary ions (clusters with two NH4 + cations and one SO42- anion) The energetics of binding and incremental association was also calculated. Double ions are not energetically favorable until 2NH3: H2SO4: 2H2O because of the about equal free energies for forming the neutral (the most stable) and double ion (the second stable) isomers. The free energy of incremental association from free H2O and 2NH3: H2SO4: nH2O has a maximum at n = 2 at room temperature with ΔG ≈ -2 kcal / mol. The comparison of incremental association energies between 2NH3: H2SO 4: nH2O, NH3: H2SO4: nH2O and H2SO4: nH2O clusters revealed that NH3 plays an important role in the atmospheric particle nucleation.