Potential energy surface and applications to carbon dioxide-water, carbon dioxide clathrate hydrate and hydrated HCl system Público
Qingfeng Wang (Spring 2018)
Published
Abstract
The potential energy surface is important to describe the molec- ular dynamics and molecular vibrations. In the first part of this thesis, an ab initio, full-dimensional, potential energy surface for CO2−H2O two-body interaction is presented. A full potential energy surface of dimer can be obtained by adding potentials for non-interacting monomers. Diffusion Monte Carlo calculations of the dimer zero-point energy are performed. Vibrational self-consistent and virtual-state configuration interaction method are used to characterize the vibrational eigenstates and energies. These results are in good agreement with experimental results. In addition, the CO2−H2O two-body potential energy surface is combined with existing water potential to develop a potential for the CO2 clathrate hydrate. A computationally efficient local-monomer treatment for this clathrate hydrate is presented. In the second part of the thesis, the vibrational predissociation of HCl−(H2O)3 cluster is studied. Using an existing potential energy surface, quasi-classical trajectory calculations were performed. This unimolecular decomposition can undergo two different pathways that were all observed by a large number of trajectory simulations. Information such as speed distribution, rotational energy distribution and branching ratio have been be obtained by analyzing final condition of the trajectories.
Table of Contents
1 Introduction................................ 1
1.1 Introduction ................................ 1
1.2 Construction of the potential energy surface . . . . . . . . . . . . . . 1
1.3 Application of the potential energy surface . . . . . . . . . . . . . . . 3
1.4 Overview of the thesis........................... 4
2 Construction and application of PES for CO2−H2O and extension to the hydrate clathrate............... 6
2.1 Introduction ................................ 6
2.2 Theory and Computational Details.................... 11
2.2.1 Ab initio electronic energies databases. . . . . . . . . . . . . . 12
2.2.2 PES2b fitting............................ 13
2.2.3 Dissociation energy and vibrational analysis of the CO2−H2O dimer................................ 15
2.2.4 CO2 hydrate clathrate....................... 17
2.3 Results and Discussion .......................... 19
2.3.1 PES2b fitting precision....................... 19
2.3.2 Properties of the CO2−H2O PES ................ 21
2.3.3 Application to CO2@(H2O)20................... 26
2.4 Summary and conclusions ........................ 30
2.5 CO2−H2O software package........................ 31
3 Vibrational predissociation of HCl−(H2O)3 . . . . . . . . 32
3.1 Introduction ................................ 32
3.2 Theoretical methods and energetics ................... 34
3.3 Results and discussion........................... 38
3.3.1 Fragment Speed Distributions................... 38
3.3.2 Fragment Rotational Energy Distributions . . . . . . . . . . . 40
3.3.3 Dissociative Trajectories and Lifetimes. . . . . . . . . . . . . . 41
3.4 Summary and conclusions......................... 45
4 Summary .................................. 46
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