Protons in polar media : an AB initio molecular dynamics study / Tycho von Rosenvinge.

Format:

Book

Manuscript

Microformat

Thesis/Dissertation

Author/Creator:

von Rosenvinge, Tycho.

Contributor:

Klein, Michael L., advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Physics.

Physics--Penn dissertations.

Local Subjects:

Penn dissertations--Physics.

Physics--Penn dissertations.

Physical Description:

xix, 156 pages : illustrations (some color) ; 29 cm

Production:

1998.

Summary:

The hydrates of hydrogen chloride are ionic crystals that contain hydronium $\rm(H\sb3O\sp+).$ The hydronium in the monohydrate has been reported to be statistically disordered between two possible sites related by inversion symmetry. Ab initio molecular dynamics calculations are presented for the monohydrate, as well as the di-, and tri-hydrates, of hydrogen chloride using the density functional based Car-Parrinello technique. The simulations were carried out with the goal of investigating proton disorder in these crystals. The possible role of nuclear quantum effects has been explored via path integral molecular dynamic simulations. The present results suggest that the proposed disordered sites in the monohydrate are dynamically unstable and therefore unlikely to be responsible for the reported disorder. No useful information was obtained for the dihydrate because the large unit cell leads to difficulties in carrying out the simulations. Nuclear quantum effects are shown to be important for characterizing the proton distributions in the trihydrate.

The structure and dynamical behavior of liquid HF with dissolved KF have been investigated using the Car-Parrinello ab initio molecular dynamics scheme. Specifically, a system with stoichiometry KF$\cdot$2HF was studied at temperatures of 400K and 1000K. This system, which was started from a phase separated mixture, rapidly formed into solvated potassium ions and H$\sb{n}$F$\sb{n+1}\sp-$ polyfluoride anions with n = 1, 2, 3, and 4. The resulting polyfluoride anions were classified, and their structures and dynamical behavior were compared with the known structures and spectra of crystalline compounds KF$\cdot x$HF and with theoretical predictions of isolated gas phase species. The present study reveals dramatic frequency shifts in the H atom vibrational modes with variation in the HF coordination number of the polyfluoride anion. In particular the FH wagging motion red shifts while the FH stretch blue shifts as n increases. The present calculations suggest that FH stretching motion infrared modes previously assigned as combination bands should likely be reinterpreted as fundamental modes of the polyfluoride anions.

This thesis describes the methods used for obtaining these results in considerable detail.

Notes:

Supervisor: Michael L. Klein.

Thesis (Ph.D. in Physics) -- University of Pennsylvania, 1998.

Includes bibliographical references.

Local Notes:

University Microfilms order no.: 98-29889.

OCLC:

187471029