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Torsional path integral Monte Carlo method for calculating the absolute quantum free energy of large molecules

Miller, Thomas F., III and Clary, David C. (2003) Torsional path integral Monte Carlo method for calculating the absolute quantum free energy of large molecules. Journal of Chemical Physics, 119 (1). pp. 68-76. ISSN 0021-9606.

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A new technique for evaluating the absolute free energy of large molecules is presented. Quantum-mechanical contributions to the intramolecular torsions are included via the torsional path integral Monte Carlo (TPIMC) technique. Importance sampling schemes based on uncoupled free rotors and harmonic oscillators facilitate the use of the TPIMC technique for the direct evaluation of quantum partition functions. Absolute free energies are calculated for the molecules ethane, n-butane, n-octane, and enkephalin, and quantum contributions are found to be significant. Comparison of the TPIMC technique with the harmonic oscillator approximation and a variational technique is performed for the ethane molecule. For all molecules, the quantum contributions to free energy are found to be significant but slightly smaller than the quantum contributions to internal energy.

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Miller, Thomas F., III0000-0002-1882-5380
Additional Information:© 2003 American Institute of Physics. Received 18 December 2002; accepted 27 February 2003. One of the authors (T.F.M.) acknowledges fellowships from the Marshall Aid Commemoration Commission and the National Science Foundation. D.C.C. acknowledges a research fellowship from the Leverhulme Trust. The work was supported by the Engineering and Physical Sciences Research Council.
Subject Keywords:organic compounds, Monte Carlo methods, free energy, harmonic oscillators, variational techniques, potential energy functions, molecular force constants
Issue or Number:1
Record Number:CaltechAUTHORS:MILjcp03
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11038
Deposited By: Archive Administrator
Deposited On:24 Jun 2008
Last Modified:03 Oct 2019 00:15

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