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An adaptive pseudospectral method for wave packet dynamics
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computational Science.
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computational Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
2012 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, 044111:1-12 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2012. Vol. 137, 044111:1-12 p.
National Category
Computational Mathematics
Identifiers
URN: urn:nbn:se:uu:diva-179058DOI: 10.1063/1.4737893ISI: 000307611500012OAI: oai:DiVA.org:uu-179058DiVA: diva2:543178
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eSSENCE
Available from: 2012-07-26 Created: 2012-08-06 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Numerical Quantum Dynamics
Open this publication in new window or tab >>Numerical Quantum Dynamics
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

We consider computational methods for simulating the dynamics of molecular systems governed by the time-dependent Schrödinger equation. Solving the Schrödinger equation numerically poses a challenge due to its often highly oscillatory solutions, and to the exponential growth of work and memory with the number of particles in the system.

Two different classes of problems are studied: the dynamics of the nuclei in a molecule and the dynamics of an electron in orbit around a nucleus. For the first class of problems we present new computational methods which exploit the relation between quantum and classical dynamics in order to make the computations more efficient. For the second class of problems, the lack of regularity in the solution poses a computational challenge. Using knowledge of the non-smooth features of the solution we construct a new method with two orders higher accuracy than what is achieved by direct application of a difference stencil.

Place, publisher, year, edition, pages
Uppsala University, 2013
Series
Information technology licentiate theses: Licentiate theses from the Department of Information Technology, ISSN 1404-5117 ; 2013-005
National Category
Computational Mathematics
Research subject
Scientific Computing
Identifiers
urn:nbn:se:uu:diva-208837 (URN)
Supervisors
Projects
eSSENCE
Available from: 2013-10-15 Created: 2013-10-08 Last updated: 2017-08-31Bibliographically approved
2. Numerical Methods for Wave Propagation: Analysis and Applications in Quantum Dynamics
Open this publication in new window or tab >>Numerical Methods for Wave Propagation: Analysis and Applications in Quantum Dynamics
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We study numerical methods for time-dependent partial differential equations describing wave propagation, primarily applied to problems in quantum dynamics governed by the time-dependent Schrödinger equation (TDSE). We consider both methods for spatial approximation and for time stepping. In most settings, numerical solution of the TDSE is more challenging than solving a hyperbolic wave equation. This is mainly because the dispersion relation of the TDSE makes it very sensitive to dispersion error, and infers a stringent time step restriction for standard explicit time stepping schemes. The TDSE is also often posed in high dimensions, where standard methods are intractable.

The sensitivity to dispersion error makes spectral methods advantageous for the TDSE. We use spectral or pseudospectral methods in all except one of the included papers. In Paper III we improve and analyse the accuracy of the Fourier pseudospectral method applied to a problem with limited regularity, and in Paper V we construct a matrix-free spectral method for problems with non-trivial boundary conditions. Due to its stiffness, the TDSE is most often solved using exponential time integration. In this thesis we use exponential operator splitting and Krylov subspace methods. We rigorously prove convergence for force-gradient operator splitting methods in Paper IV. One way of making high-dimensional problems computationally tractable is low-rank approximation. In Paper VI we prove that a splitting method for dynamical low-rank approximation is robust to singular values in the approximation approaching zero, a situation which is difficult to handle since it implies strong curvature of the approximation space.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 33 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1330
Keyword
computational wave propagation, quantum dynamics, time-dependent Schrödinger equation, spectral methods, Gaussian beams, splitting methods, low-rank approximation
National Category
Computational Mathematics
Research subject
Scientific Computing
Identifiers
urn:nbn:se:uu:diva-268625 (URN)978-91-554-9437-7 (ISBN)
Public defence
2016-02-12, ITC 2446, Lägerhyddsvägen 2, Uppsala, 10:15 (English)
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Supervisors
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eSSENCE
Available from: 2016-01-19 Created: 2015-12-08 Last updated: 2016-02-12

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