Linear water dimer

Table 2. Interaction energies vs physical model for the C, linear water dimer (Millot-Stone basis set). 

Various energy terms calculated for the linear water dimer molecule and for some hexamer water clusters at the HF level in both the canonical and the separated representations, using various basis sets are given in the present work. This study is twofold. First, the differences between the proton donor and proton acceptor molecules have been assessed in the linear water dimer. The EM energy contributions (obtained in the separated representation) are expected to characterize the proton donor / acceptor ability of the monomers. Secondly, a possibility of identification of a proton donor or acceptor character of the monomers in some water hexamers was tested. 

Results obtained for a linear water dimer structure... 

Following the analysis of the characteristic features determined for the proton donor and acceptor molecules in a linear water dimer, we performed the same study for some water hexamer clusters. The structures considered are representative of those published in a previous paper [18]. 

In this work the separated representation was used to determine the energetic quantities for each contributing monomer in some water hexamer systems, too. On one hand, the results obtained for the monomers in these structures did not suggest to identify the same proton donor or acceptor nature as it was found for the linear water dimer. On the other hand, in three of the water hexamer structures that were investigated, some monomers showed a specific nature. These results confirm previous results [18] that there are extra interaction abilities in these hexamer structures (prism, w6t and w6q). 

Table 2.23 Equilibrium geometries and binding energies (uncorrected for BSSE) calculated for the linear water dimer at various levels of theory. ...

When two molecules interact, there is often a small amount of electron flow from one to the other. For example, in the equilibrium geometry of the linear water dimer HO— H... OH2, the water molecule that is the proton acceptor has transferred about 0.05e to the proton donor water (9,10). The attractive energy associated with this charge transfer is the charge transfer energy and can be thought of as a mixing of an ionic resonance structure... 

Magnasco, V. and Musso, G.F. (1981) H2-H2 revisited. Orthogonalization, polarization and delocalization effects within a bond-orbital scheme. Chem. Phys. Lett., 84, 575-579. Magnasco, V., Musso, G.F., Costa, C., andFigari, G. (1985) A minimal basis bond-orbital investigation of the linear water dimer. Mol. Phys., 56, 1249-1269. 

Geometry optimisations were performed for linear water dimers, where the 0-H...0 hydrogen bond is constrained to be linear (see Figure 2 for a definition of the relevant parameters). The water dimers were first constructed using the same water model for donor... 

In Table 2 we present the binding energies and structures for the linear water dimers obtained with the different water models and the different water model combinations. 

Table 2 Geometry and binding energy for optimised linear water dimers...

Table 1 Optimized Geometrical Parameters of Linear Water Dimer Computed at SCF and MP2 Levels with Various Basis Sets " ...

Linear water dimer. The earliest example we considered dating back from the mid-eighties is the linear water dimer at equilibrium distance (doo = 2.95 A) [93, 94]. We monitored the evolutions, as a function of the theta angle, of AE... 

Fig. 1.1 Linear water dimer. Compared evolutions of a AE (SIBFA), AE(HF), and Emtp full, dashed, and dotted lines, respectively b Eexch(HF). and Erep(SIBFA) (full and dashed lines), and c Ect(HF) and Ect(SIBFA) (full and dashed lines). The dotted and dashed-dotted lines represent the contributions to Ect(SIBFA) from each of the two individual sp lone pairs of the donor oxygen. Reprinted with permission from Gresh et al. [94]. Copyright 1986 Wiley...

Linear water dimer is unstable on the MM2 potential surface. It collapses to a bifurcated water dimer. 

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