| 1. |
- Poulsen, Jens Aage, 1972, et al.
(author)
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Dynamics of Gaussian Wigner functions derived from a time-dependent variational principle
- 2017
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In: AIP Advances. - : AIP Publishing. - 2158-3226. ; 7
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Journal article (peer-reviewed)abstract
- © 2017 Author(s). By using a time-dependent variational principle formulated for Wigner phase-space functions, we obtain the optimal time-evolution for two classes of Gaussian Wigner functions, namely those of either thawed real-valued or frozen but complex Gaussians. It is shown that tunneling effects are approximately included in both schemes.
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| 2. |
- Svensson, S. Karl-Mikael, 1990, et al.
(author)
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Calculation of reaction rate constants from a classical Wigner model based on a Feynman path integral open polymer
- 2021
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In: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 152:9
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Journal article (peer-reviewed)abstract
- The Open Polymer Classical Wigner (OPCW) method [J. Chem. Phys. 152, 094111 (2020)] is applied to a flux-Heaviside trace for calculating reaction rate constants. The obtained expression for the reaction rate constant is tested on a symmetric Eckart potential. The OPCW method is shown to converge toward the exact classical Wigner result. The OPCW method shows some promise for rate constant calculations and suggestions for future tests are made.
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| 3. |
- Svensson, S. Karl-Mikael, 1990, et al.
(author)
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Classical Wigner model based on a Feynman path integral open polymer
- 2020
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:9
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Journal article (peer-reviewed)abstract
- The classical Wigner model is one way to approximate the quantum dynamics of atomic nuclei. Here, a new method is presented for sampling the initial quantum mechanical distribution that is required in the classical Wigner model. The new method is tested for the position, position-squared, momentum, and momentum-squared autocorrelation functions for a one-dimensional quartic oscillator and double well potential as well as a quartic oscillator coupled to harmonic baths of different sizes. Two versions of the new method are tested and shown to possibly be useful. Both versions always converge toward the classical Wigner limit. For the one-dimensional cases, some results that are essentially converged to the classical Wigner limit are acquired and others are not far off. For the multi-dimensional systems, the convergence is slower, but approximating the sampling of the harmonic bath with classical mechanics was found to greatly improve the numerical performance. For the double well, the new method is noticeably better than the Feynman–Kleinert linearized path integral method at reproducing the exact classical Wigner results, but they are equally good at reproducing exact quantum mechanics. The new method is suggested as being interesting for future tests on other correlation functions and systems.
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| 4. |
- Svensson, S. Karl-Mikael, 1990, et al.
(author)
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Formation of the Hydroxyl Radical by Radiative Association
- 2015
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 119:50, s. 12263-12269
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Journal article (peer-reviewed)abstract
- The reaction rate constant for the radiative association of O(3P) and H(2S) has been calculated by combining a few different methods and taking account of both direct and resonance-mediated pathways. The latter includes both shape resonances and Feshbach type inverse predissociation. The reaction rate constant is expressed as a function of temperature in the interval 10−30000 K. This reaction may be astrochemically relevant and is expected to be of use in astrochemical networks.
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| 5. |
- Svensson, S. Karl-Mikael, 1990
(author)
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Quantum dynamical effects in complex chemical systems
- 2020
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Doctoral thesis (other academic/artistic)abstract
- When using mathematical models to computationally investigate a chemical system it is important that the methods used are accurate enough to account for the relevant properties of the system and at the same time simple enough to be computationally affordable. This thesis presents research that so far has resulted in three published papers and one unpublished manuscript. It concerns the application and development of computational methods for chemistry, with some extra emphasis on the calculation of reaction rate constants. In astrochemistry radiative association is a relevant reaction mechanism for the formation of molecules. The rate constants for such reactions are often difficult to obtain though experiments. In the first published paper of the thesis a rate constant for the formation of the hydroxyl radical, through the radiative association of atomic oxygen and hydrogen, is presented. This rate constant was calculated by a combination of different methods and should be an improvement over previously available rate constants. In the second published paper of this thesis two kinds of basis functions, for use with a variational principle for the dynamics of quantum distributions in phase space, i.e. Wigner functions, is presented. These are tested on model systems and found to have some appealing properties. The classical Wigner method is an approximate method of simulation, where an initial quantum distribution is propagated in time with classical mechanics. In the third published paper of this thesis a new method of sampling the initial quantum distribution, with an imaginary time Feynman path integral, is derived and tested on model systems. In the unpublished manuscript, this new method is applied to reaction rate constants and tested on two model systems. The new sampling method shows some promise for future applications.
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