Water dimer structure

Figure 5.38 displays the optimized structure and primary npt— ooh donor-acceptor interaction of the complex (5.70a) in which PtH2 serves as the Lewis-base donor. The qualitative similarity to the water dimer structure (Fig. 5.5(b)) is immediately apparent, including the short Pt H distance (2.47 A, more than 0.5 A inside van der Waals contact), the roughly linear Pt H—O angle (161°), and the characteristic elongation of the H-bonded versus free O—H bond of the water monomer (by 0.01 A). The leading nPt a0H donor-acceptor interaction in Fig. 5.38(b) is... 

FIG. 3 The vapor phase water dimer structure. Polar covalent bonds are shown as solid lines and the hydrogen bond as a dashed line (adapted from Ludwig, 2001). 

Results obtained for a linear water dimer structure... 

It is worthwhile analyzing whether the same conclusion holds when the water dimer structure is considered. A series of calculations have been performed for a linear structured water dimer, the values are listed in Table II. 

Figure 10 gives the results for the water dimer. The optimized water dimer structure also compared well with recent gas-phase experimental data on the gas water dimer by Dyke (1984) r00 = 2.98A and tilt angle = 123°. The energy obtained in forming the hydrogen bond is given in Table 2. 

MBE 880du The hfs of various tunneling states is fitted to suitably defined spin-rotation and spin-spin interaction strengths. The latter are discussed in terms of the water dimer structure. 

Hg. 6.13 Minimum energy structure for water dimer with TIP3P model... 

Optimizing water dimer can be challenging in general, and DFT methods are known to have difficulty with weakly-bound complexes. When your optimization succeeds, make sure that you have found a minimum and not a transition structure by verifying that there are no imaginary frequencies. In the course of developing this exercise, we needed to restart our initial optimization from an improved intermediate step and to use Opt=CalcAII to reach a minimum. 

Y ater dimer distance variation provides a sequence of structures for water dimer at different nonbonded OH distances. Plot energy (vertical axis) vs. nonbonded OH distance (horizontal axis). What is the optimum distance How much energy is required to increase this distance by 10% How much is required to reduce the distance by 10% Are the two distortion energies about the same magnitude If not, explain why not. 

Dyke, T.R., Mack, K.M. and Muenter, J.S. (1977) The structure of water dimer from molecular beam electric resonance spectroscopy, J. Chem. Phys., 66,498-510. 

The dimeric structure of the NifS CsdB protein includes two distinct PLP-containing active sites per dimer, but the two active sites are spatially separated and apparently autonomous. We therefore used only the monomer and surrounding water molecules in the calculations. The entire model consists of 7992 atoms with 84 atoms from the active-site selected as the model part and treated quantum mechanically. 

Another important question deals with the intramolecular and unimolecular dynamics of the X-—RY and XR -Y- complexes. The interaction between the ion and molecule in these complexes is weak, similar to the intermolecular interactions for van der Waals molecules with hydrogen-bonding interactions like the hydrogen fluoride and water dimers.16 There are only small changes in the structure and vibrational frequencies of the RY and RX molecules when they form the ion-dipole complexes. In the complex, the vibrational frequencies of the intramolecular modes of the molecule are much higher than are the vibrational frequencies of the intermolecular modes, which are formed when the ion and molecule associate. This is illustrated in Table 1, where the vibrational frequencies for CH3C1 and the Cr-CHjCl complex are compared. Because of the disparity between the frequencies for the intermolecular and intramolecular modes, intramolecular vibrational energy redistribution (IVR) between these two types of modes may be slow in the ion-dipole complex.16... 

Besides water dimer, larger clusters of water molecules were extensively investigated by means of the DFT calculations87 111 114 127 128. Laasonen et al.113 studied the structure, the energies, and the vibrational frequencies of small water clusters (up to eight molecules)... 

Odutola, J. A., and T. R. Dyke. 1980. Partially deuterated water dimers Microwave spectra and structure. J. Chem. Phys. 72, 5062. 

Bandyopadhyay, P. Ten-No, S. Iwata, S., Ab initio Monte Carlo simulation using multicanonical algorithm temperature dependence of the average structure of water dimer, Mol. Phys. 1999, 96, 349-358... 

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