Global Search for Minimum Energy (H₂O)_n Clusters, n = 3−5

Abstract

The Gaussian-3 (G3) model chemistry method has been used to calculate the relative deltaG(o) values for all possible conformers of neutral clusters of water, (H2O)n, where n = 3-5. A complete 12-fold conformational search around each hydrogen bond produced 144, 1728, and 20,736 initial starting structures of the water trimer, tetramer, and pentamer. These structures were optimized with PM3, followed by HF/6-31G* optimization, and then with the G3 model chemistry. Only two trimers are present on the G3 potential energy hypersurface. We identified 5 tetramers and 10 pentamers on the potential energy and free-energy hypersurfaces at 298 K. None of these 17 structures were linear; all linear starting models folded into cyclic or three-dimensional structures. The cyclic pentamer is the most stable isomer at 298 K. On the basis of this and previous studies, we expect the cyclic tetramers and pentamers to be the most significant cyclic water clusters in the atmosphere.

Prediction of Accurate Anharmonic Experimental Vibrational Frequencies for Water Clusters, (H2O)n, n = 2−5

“…Figure 1 displays the most stable structures of the water trimer, water tetramer, and water pentamer at 298K. 72 The labeling of the waters in the figures will be used to uniquely identify the vibrational modes described in the tables. For the trimer the "u", "d", and "a" labels refer to the unique, donor, and acceptor water molecules in this cluster.…”

“…72 In our previous work on the water dimer we have shown thatHF/6-31G* frequencies scaled by 0.8929 have a 24 cm -1 root-mean-square deviation (RMSD) from experiment, while combining scaled frequencies for the intramolecular modes with anharmonic frequencies for the intermolecular modes improves the RMSD to 20 cm -1 . 72 We now extend this work to include water clusters containing three to five water molecules, with a goal of providing experimentalists reliable values to aid in their search for these clusters in the gas phase. We make use of Barone's recently implemented second-order perturbation approach to obtain anharmonic frequencies.…”

Wavefunction methods for the accurate characterization of water clusters

“…169 Many other stationary points exist on the (H 2 O) 4 PES, such as bicyclic structures and double hydrogen bond donor arrangements, but they have significantly higher electronic energies. 169,170 Interestingly, the δ…”

Supramolecular Encapsulation of Tetrahedrally Hydrated Guests in a Tetrahedron Host

“…[9,10] Recently, an elegant example of a lone water molecule in the fullerene C 60 was reported. [11] However, such a tetrahedral array for a discrete pentamer cluster enclosed in a capsule-like host, [12,13] has not previously been observed.…”