FU Berlin Digitale Dissertation
Lorenzo Pesce  : Dissipative Quantum Dynamics of Elementary Chemical Processes at Metal Surfaces Dissipative Quantendynamik elementarer chemischer Prozesse an Metalloberflächen
|Abstract| |Table of Contents| |More Information|

Abstract Almost all important chemical reactions take place in the condensed phase, e.g., in solution or at catalytic surfaces. Even the reactions between gases are often mediated by a surface, like the Haber-Bosch synthesis of ammonia. Our efforts were directed towards the extension of the models and tools used in gas phase quantum dynamics to condensed phases, in particular with regards to reactions on/with surfaces. Quantum systems in the condensed phase are usually modeled within open system density matrix theory. This kind of calculations are very demanding and it is only very recently that they have been considered in computational chemistry. Consequently, a necessary step was to find and develop methods that allow for the efficient propagation of density matrices according to the Liouville-von Neumann equation. First, we worked on the implementation of polynomial integrators. Among them, we developed a new algorithm to compute absorption spectra for molecules in a condensed phase environment. We applied this method successfully to the computation of the infrared absorption spectrum of benzoic acid dimers in benzoic acid crystals. Using polynomial integrators, we studied also the dynamics of H2 and isotopomers scattering from metal surfaces. This is a prototype system to model an elementary step of surface catalysis: The molecules reach the surface and there change their state. We started simulating the scattering of a thermal gas from a rigid copper surface, where we found a marginal yet interesting inelastic deexcitation of vibrationally "hot" H2 (D2) impinging an inert surface. Then, we studied the scattering of vibrationally excited H2 molecules and isotopomers from metal surfaces, this time with a surface that can exchange energy with the molecule. Here, we have shown evidence that the large vibrational deexcitation of H2 seen in the experiments done in the group of Sitz cannot be explained simply on the basis of a coupling to the surface electrons and/or phonons, and we conclude that also the other degrees of freedom of H2 should be taken into account. The dissipation model we introduced implies interesting isotope effects and an almost complete independence of the results on the kinetic energy of the impinging H2 molecule. This should stimulate interesting experimental comparisons. To compute the scattering of H2 at metal surfaces that are not kept "frozen", we had to develop a new method: The Coupled Channel Density Matrix (CCDM) method, which allows for the multi dimensional density matrix propagation including unbound modes. We finally investigated NO photodesorption from Pt(111) surfaces using the scheme recently introduced by U. Manthe, called Variational Wave Packet (VWP) method. We investigated its performance with respect to dissociative problems (before it was applied only to bound models), for which we computed up to two dimensional systems, which are not tractable with direct density matrix calculations. This method is very promising for large scale calculations because of its generality and the effcient use of memory in computer simulations.

Table of Contents Download the whole PhDthesis as a zip-tar file or as zip-File For download in PDF format click the chapter title Cover and Contents Notations and conventions 1 Introduction 1.1 General introduction 1.2 Structure of the thesis 2 Outline of density matrix theory 2.1 The concept of a density matrix 2.2 Equations of motion 3 Numerical methods to solve the Liouville-von Neumann equation 3.1 Integration the Liouville-von Neumann equation: Direct and indirect approches 3.2 Polynomial Expansions 3.3 Calculation of absorption spectra of benzoic acid dimers 3.4 The Variational Wave Packet (VWP) method 4 Photoinduced desorption of NO from Pt(111) 4.1 NO photodesorption and the Variational Wave Packet scheme 4.2 One dimensional model 4.3 Two dimensional model 5 H2 scattering from noble metal surfaces 5.1 Introduction: the H2/metal system 5.2 The Coupled Channel Density Matrix (CCDM) method 5.3 Numerical performance of the method 5.4 Inelastic molecule surface scattering 5.5 Dissipative dynamics with the CCDM method 5.6 Numerical implementation 5.7 Dynamics of D2(H2) (m = 1) at nondissociative, cold metal surfaces 6 Conclusions and outlook A Kinetic energy evaluation A.1 DVR and FFT methods A.2 DVR versus FFT for CCDM calculations B Implementation of the dissipative CCDM equations Bibliography

More Information:
Online available:	http://darwin.inf.fu-berlin.de/1998/4/indexe.html
Language of PhDThesis:	english
Keywords:	Dissipation; quantum dynamics; surface; density matrix; numerical methods; hydrogen
DNB-Sachgruppe:	30 Chemie
Classification PACS:	76.60
Date of disputation:	22-Jul-98
PhDThesis from:	Department Chemie, Freie Universität Berlin
First Referee:	Priv-doz. Dr. Peter Saalfrank
Second Referee:	Prof. Dr. Jörn Manz
Contact (Author):	fish@chemie.fu-berlin.de
Contact (Advisor):	saalfran@chemie.fu-berlin.de
Date created:	07-Dec-98
Date available:	23-Jun-99

 

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