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- Poulsen, Jens Aage, 1972, et al.
(författare)
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Determination of the Van Hove spectrum of liquid He(4): An application of the Feymnan-Kleinert linearized path integral methodology
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:41, s. 8743-8751
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Tidskriftsartikel (refereegranskat)abstract
- The spectrum of the Van Hove correlation function (CF) is calculated for liquid He(4) at 27 K and a density of 0.25 g/cm(3) by utilizing a recently proposed approximation to quantum CFs derived by combining an effective-frequency Boltzmann-Wigner transform with a linearized path integral expression for CFs. For this anharmonic system and highly nonlinear CF, we obtain excellent agreement with available accurate results. In particular, the first, second, and third moments of the spectrum are in very good agreement with both experiment and earlier theoretical results. Also, the calculated kinetic energy is in excellent agreement with accurate path integral Monte Carlo results.
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| 2. |
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| 3. |
- Poulsen, Jens Aage, 1972, et al.
(författare)
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Quantum diffusion in liquid para-hydrogen: An application of the Feymnan-Kleinert linearized path integral approximation
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:51, s. 19799-19808
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Tidskriftsartikel (refereegranskat)abstract
- Quantum effects on diffusion in liquid para-hydrogen at temperatures of T = 17 and 25 K and saturated vapor pressure is studied by calculating the diffusion coefficient from the standard Green-Kubo formula, using both the ordinary velocity correlation function (CF) and its Kubo-transformed counterpart. All CFs are calculated with a recently proposed linearized path integral expression for general CFs, using an approximate Wigner transformed Boltzmann operator based on Feynman-Kleinert variational path integral theory. Also, the ability of the approximate Wigner transform to predict the radial distribution function and kinetic energy of the liquid is investigated. The conclusions are as follows: (i) The predicted structure of liquid parahydrogen is in excellent agreement with accurate path integral Monte Carlo calculations at both temperatures. (ii) The calculated liquid kinetic energy is in very good agreement with the accurate value at T = 25 K but deviates somewhat from the accurate value at T = 17 K. (iii) The diffusion coefficients based on the Kubo-transformed CF are in very good agreement with experiment, at both temperatures, whereas results from the ordinary velocity CF are not accurate at T = 17 K. The reason for the better performance of the Kubo CF approach is attributed to the latter's robustness toward errors in the approximate Boltzmann operator Wigner transform. The kinetic energy derived from the Kubo-transformed CFs is in excellent agreement with accurate values at both temperatures.
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| 4. |
- Poulsen, Jens Aage, 1972, et al.
(författare)
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Wave Packet Study of Ultrafast Relaxation in Ice Ih and Liquid Water. Resonant Intermolecular Vibrational Energy Transfer
- 2003
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Ingår i: J. Phys. Chem A. - : American Chemical Society (ACS). ; 107, s. 8420-8428
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Tidskriftsartikel (refereegranskat)abstract
- By using quantum chemistry, the fundamental normal modes and the frequencies of ice Ih and room-temperature water clusters containing up to 15 water molecules are constructed. These normal modes are then used on the basis of assumed harmonic dynamics for analyzing the survival probability and energy decay of wave packets which reflect symmetric and asymmetric stretch excitations in single water molecules. Following symmetric stretch excitation, it is found that the wave packet survival probability and the OH stretch mode energy both decay on a sub-100-fs time scale in both phases. For asymmetric stretch excited states, the characteristic relaxation time is below 100 fs in ice Ih, but it is slower in liquid water. In both cases, it is found that the dynamics are truly many-body in character, since clusters of size ~15 are required to converge the early time behavior of the OH mode relaxation processes. The results support the suggestion of Woutersen and Bakker (Nature 1999, 402, 507-509) that, in liquid water, intermolecular vibrational energy transfer occurs on a sub-100-fs time scale. The dynamics appear to be predominantly of harmonic character.
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