Neutron Scattering Of Hydrogen Bonds In Ice And The Amino Acid Hydration And First Principles

In this dissertation, the mechanism of the hydrogen bond in ice and the amino acids hydrate has been investigated by ab initio molecular dynamics simulations combined with inelastic incoherent neutron scattering technique.By means of ab initio molecular dynamics simulations we firstly reproduced the two optic peaks at 27 and 36 meV in the inelastic incoherent neutron scattering (IINS) spectrum of ice Ih. By calculating the vibrational spectrum for each hydrogen atom, we found that there exist at least two peaks in the low energy transfer of the spectrum, for any hydrogen atom both along the c axis and in the plane ab. This coincides with the experimental results that there are no differences between the two IINS spectra obtained with neutron beam parallel and perpendicular to c axis respectively. Our calculated results confirmed that the two optic peaks are independent of the crystalline orientation. We also have studied the relationship between the 00 separations and the hydrogen bond strengths by analyzing the vibrational spectrum for several different lattice parameters. With the decreasing lattice parameters, the H-bond length decreases, consequently the H-bond strength increases, and the position of peaks of H-bond shift to the higher frequencies, whereas the 0-H stretching frequencies move to the lower ones.The vibrational spectrum of ice VIII in the low frequency is not the same as that of other phases of ice, whose H-bond peaks just exist below 30 meV. Using ab initio molecular dynamics simulations we also obtained the vibrational spectrum of ice VIII. In our calculated vibrational spectrum there exists just one peak in low energy range, which proved that there is only one weak hydrogen bond in ice VIII. By comparing all the H-bond lengths in different phases of ice, we concluded that it is due to much longer H-bond lengths in ice VIII than in other phases that the H-bond peak of ice VIII appears just below 30 meV.By applying inelastic incoherent neutron scattering and ab initio molecular dynamics simulations, we investigated the hydrogen bonding interactions between water and some amino acids (glycine, L-glutamine, L-threonine, L-cysteine and...