Theoretical Study of Microscopic Solvation of Ammonia in Water Clusters:  NH₃(H₂O)_n,n= 3, 4

Abstract

A number of significant structures of NH3(H2O) n (n = 3, 4) clusters have been identified by ab initio Monte Carlo simulated annealing, a procedure that efficiently samples minima on a potential energy surface. In this procedure, energies were computed ab initio at each Monte Carlo step by the B3-LYP density functional method with the 6-31G* basis set. All geometries of the isomers found for each cluster were refined in full conventional geometry optimizations, and frequency analyses were performed at both the B3-LYP and MP2 levels with the 6-311+G(d,p) basis set. The B3-LYP and MP2 energy orders were confirmed with single point QCISD(T) calculations with the 6-311+G(d,p) basis set performed on the MP2 optimized geometries. Only associated isomers were found for NH3(H2O)3. However, for NH3(H2O)4 both associated and dissociated structures were found.

Interaction between PH3 and small water clusters: Understanding the electronic and spectroscopic properties

“…The highest difference observed in the results reported by Bacelo [14] may be due to the methodology applied in his study. The study of Bacelo [14] calculated the electronic energy using B3LYP/6-311+G(d, p) and MP2/6-311+G(d, p) with the inclusion of the BSSE correction. On the other hand, Pratihar and Chandra [16] For the complexes with four water molecules, i4c has the highest relative energy compared to i4a, and the energy gap is 4.2 kcal mol À1 compared to i4b using CCSD(T)/6-311++G(2df, 2pd).…”

“…Furthermore, it is important to note that the double hybrid functionals correctly describe the stability of the isomers without long-range dispersion corrections. The results for the NH 3 (H 2 O) 3 clusters reported by Bacelo [14] and Pratihar and Chandra [16] indicate that the energy difference between the isomers varied from 2.58 to 7.36 kcal mol À1 . The highest difference observed in the results reported by Bacelo [14] may be due to the methodology applied in his study.…”

“…The results for the NH 3 (H 2 O) 3 clusters reported by Bacelo [14] and Pratihar and Chandra [16] indicate that the energy difference between the isomers varied from 2.58 to 7.36 kcal mol À1 . The highest difference observed in the results reported by Bacelo [14] may be due to the methodology applied in his study. The study of Bacelo [14] calculated the electronic energy using B3LYP/6-311+G(d, p) and MP2/6-311+G(d, p) with the inclusion of the BSSE correction.…”

“…No frequency scale factor was used for the vibrational frequencies or the zero-point vibrational energy (ZPVE). It is important to note that the studied phosphine-water structures are based on the analogous ammonium complexes [11][12][13][14][15][16][17][18][19].…”

“…Recently, Lane and Kjaergaard [11] also characterized the phosphine-water complex at a high level of theory using the CCSD(T)-F12 and CCSD(T) methods. For the analogous ammonium-water clusters [NH 3 (H 2 O) n ], a very different picture emerges due to the rich source information on these complexes [12][13][14][15][16][17][18][19][20][21]. The limited information on phosphine-water complexes due to a lack of any experimental data emphasizes the need to evaluate the electronic properties of the interaction between phosphine and more than one water molecule.…”