Structure of the interlayer in normal 11 Å tobermorite from an ab initio study

The structural positions and dynamics of water molecules in the interlayer of normal 11 Å tobermorite were analyzed based on ab initio molecular dynamics simulations. The calculated structural parameters of the tobermorite building blocks are in good agreement with the results of X-ray diffraction and EXAFS measurements. The simulations provide detailed information on the structure of the hydrogen bonding network formed by water molecules, the OH groups, and the coordination of interlayer Ca ions. Structural position of W1, W2 and W3 sites non-bonded to the interlayer Ca ions were found to be similar to the corresponding sites in the anomalous 11 Å tobermorite. These molecules undergo a slow rotational motion at the position of their equilibria. The H₂O molecules forming coordination shell of interlayer Ca ions have a fixed orientation that is constrained by strong hydrogen bonds to neighbouring oxygen sites. The IR spectrum of natural 11 Å tobermorite was interpreted based on the calculated vibrational density of state.