Water dimer system

Korchowiec J, Uchimaru T (2000) New energy partitioning scheme based on the self-consistent charge and configuration method for subsystems application to water dimer system. J Chem Phys 112(4) 1623—1633... 

A question arises, whether the various energy quantities derived by the SMO method could yield useful information on the monomer s role (proton donor or acceptor) in the weakly interacting water dimer system. 

The PES of the water dimer system is characterised by three main stationary points the "quasi-linear" structure, representing the global minimum (Fig. 11), and the cyclic and bifurcated configurations (saddle points). 

Fig. 11 Transilinear Cs minimum energy geometry of the water dimer system. The relevant intermolecular coordinates are indicated.

Partitioning Scheme Based on the Self-Consistent Charge and Configuration Method for Subsystems Application to Water Dimer System. 

Optimised geometrical parameters for the water dimer system (see Fig 2). 

One after the other, examine methanol dimer and acetic acid dimer. Do the hydrogen-bond lengths in these systems differ significantly from the optimum distance in water dimer Are the hydrogen-bond angles in these compounds significantly different from those in water dimer Rationalize your results. 

One additional important reason why nonbonded parameters from quantum chemistry cannot be used directly, even if they could be calculated accurately, is that they have to implicitly account for everything that has been neglected three-body terms, polarization, etc. (One should add that this applies to experimental parameters as well A set of parameters describing a water dimer in vacuum will, in general, not give the correct properties of bulk liquid water.) Hence, in practice, it is much more useful to tune these parameters to reproduce thermodynamic or dynamical properties of bulk systems (fluids, polymers, etc.) [51-53], Recently, it has been shown, how the cumbersome trial-and-error procedure can be automated [54-56A],... 

The water dimer is probably the most intensively studied intermolecular hydrogen bonded system of all. Hence, ample theoretical and experimental data is available for this system,... 

A water dimer, which bears more relevance to biological systems, was recently investigated by many researchers. Results obtained using various implementations of the Kohn-Sham formalism were reported.87 109-116 119 122 124 125 128 Table 4.2 collects selected results. 

Suhai128 investigated water dimer and an infinite chain of hydrogen-bonded water molecules by means of the DFT and post-Hartree-Fock calculations. For the infinite system, the DFT(BLYP), MP2, and MP4 binding energies were within 0.2 kcal/mol, whereas the corresponding interatomic distances were within 0.04 A. A similar agreement was reported for water dimer. 

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). 

The discussion of porphyrin complexes in the activation of dioxygen in solution can be readily subdivided into discussions of monomeric systems and dimeric systems. The dimeric systems (cofacial metallodi-porphyrins) have recently been reviewed by Collman, Wagenknecht, and Hutchison (73). That review highlights the significant amount of research stimulated by the initial discovery by Collman and co-workers (74), confirmed later by Chang and co-workers (75), that dicobalt cofacial diporphyrins can promote the direct four-electron reduction of dioxygen to water. 

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