Structural position of H2O molecules and hydrogen bonding in anomalous 11 angstrom tobermorite

For the first time, the structure and dynamics of H2O in the interlayer of anomalous 11 angstrom tobermorite have been analyzed based on ab initio molecular dynamics simulations. The simulations provide detailed information on the structure of the hydrogen bonds formed by H2O molecules and OH groups. The calculated structural parameters of the tobermorite building blocks are in good agreement with the experimental model of Merlino et al. (1999), which is based on X-ray diffraction (XRD) Measurements. However, in contrast to the measurements, the simulations suggest that the W1 and W3 sites are split between two general positions with 50% occupancy. It is proposed that the experimental studies provide only averaged coordinates of these sites due to the limitations imposed by the polytypic structures. Analysis of the H2O dynamics at 321 and 506 K suggest the possibility of a temperature induced order-disorder transition associated with the orientation of O6H center dot center dot center dot W1 and O6H center dot center dot center dot W3 hydrogen bonds in the structure of anomalous 11 angstrom tobermorite. The experimental IR and Raman spectra of 11 angstrom tobermorite are interpreted based on analyses of the vibrational density of stales.