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How accurate is molecular dynamics?
Weierstrass Institute for Applied Analysis and Stochastics.
KTH, School of Computer Science and Communication (CSC), Numerical Analysis, NA (closed 2012-06-30).
KTH, School of Computer Science and Communication (CSC), Numerical Analysis, NA (closed 2012-06-30).
Dept. of Mathematical Sciences, University of Delaware.
Show others and affiliations
2012 (English)Report (Other academic)
Abstract [en]

Born-Oppenheimer dynamics is shown to provide an accurate approximation of time-independent Schrödinger observables for a molecular system with an electron spectral gap, in the limit of large ratio of nuclei and electron masses, without assuming that the nuclei are localized to vanishing domains. The derivation, based on a Hamiltonian system interpretation of the Schrödinger equation and stability of the corresponding hitting time Hamilton-Jacobi equation for non ergodic dynamics, bypasses the usual separation of nuclei and electron wave functions, includes caustic states and gives a different perspective on theBorn-Oppenheimer approximation, Schrödinger Hamiltonian systems and numerical simulation in molecular dynamics modeling at constant energy.

Place, publisher, year, edition, pages
2012. , 47 p.
Series
TRITA-NA, ISSN 0348-2952 ; 2012:8
Keyword [en]
Born-Oppenheimer approximation, WKB expansion, caustics, Fourier integral operators, Schrödinger operators
National Category
Mathematical Analysis Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-94125OAI: oai:DiVA.org:kth-94125DiVA: diva2:525383
Funder
Swedish e‐Science Research Center
Note

QC 20120508

Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2016-12-22Bibliographically approved
In thesis
1. Complexity and Error Analysis of Numerical Methods for Wireless Channels, SDE, Random Variables and Quantum Mechanics
Open this publication in new window or tab >>Complexity and Error Analysis of Numerical Methods for Wireless Channels, SDE, Random Variables and Quantum Mechanics
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis consists of the four papers which consider different aspects of stochastic process modeling, error analysis, and minimization of computational cost.

     In Paper I, we construct a Multipath Fading Channel (MFC) model for wireless channels with noise introduced through scatterers flipping on and off. By coarse graining the MFC model a Gaussian process channel model is developed. Complexity and accuracy comparisons of the models are conducted.

     In Paper II, we generalize a multilevel Forward Euler Monte Carlo method introduced by Mike Giles for the approximation of expected values depending on solutions of Ito stochastic differential equations. Giles' work proposed and analyzed a Forward Euler Multilevel Monte Carlo (MLMC) method based on realizations on a hierarchy of uniform time discretizations and a coarse graining based control variates idea to reduce the computational cost required by a standard single level Forward Euler Monte Carlo method. This work is an extension of Giles' MLMC method from uniform to adaptive time grids. It has the same improvement in computational cost and is applicable to a larger set of problems.

     In paper III, we consider the problem to estimate the mean of a random variable by a sequential stopping rule Monte Carlo method. The performance of a typical second moment based sequential stopping rule is shown to be unreliable both by numerical examples and by analytical arguments. Based on analysis and approximation of error bounds we construct a higher moment based stopping rule which performs more reliably.

     In paper IV, Born-Oppenheimer dynamics is shown to provide an accurate approximation of time-independent Schrödinger observables for a molecular system with an electron spectral gap, in the limit of large ratio of nuclei and electron masses, without assuming that the nuclei are localized to vanishing domains. The derivation, based on a Hamiltonian system interpretation of the Schrödinger equation and stability of the corresponding hitting time Hamilton-Jacobi equation for non ergodic dynamics, bypasses the usual separation of nuclei and electron wave functions, includes caustic states and gives a different perspective on the Born-Oppenheimer approximation, Schrödinger Hamiltonian systems and numerical simulation in molecular dynamics modeling at constant energy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vii, 65 p.
Series
Trita-CSC-A, ISSN 1653-5723 ; 2012:06
Keyword
Wireless Channels; SDE; Monte Carlo Methods, Molecular Dynamics, Quantum Mechanics
National Category
Computational Mathematics Probability Theory and Statistics
Identifiers
urn:nbn:se:kth:diva-94150 (URN)978-91-7501-350-3 (ISBN)
Public defence
2012-05-30, F3, Lindstedtsvägen 26, Kungliga Tekniska högskolan, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20120508

Available from: 2012-05-08 Created: 2012-05-08 Last updated: 2013-04-09Bibliographically approved

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