Huang, Shao-Nung and Pascal, Tod A. and Goddard, William A., III and Maiti, Prabal K. and Lin, Shiang-Tai (2011) Absolute Entropy and Energy of Carbon Dioxide Using the Two-Phase Thermodynamic Model. Journal of Chemical Theory and Computation, 7 (6). pp. 1893-1901. ISSN 1549-9626 http://resolver.caltech.edu/CaltechAUTHORS:20110627-164401296
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The two-phase thermodynamic (2PT) model is used to determine the absolute entropy and energy of carbon dioxide over a wide range of conditions from molecular dynamics trajectories. The 2PT method determines the thermodynamic properties by applying the proper statistical mechanical partition function to the normal modes of a fluid. The vibrational density of state (DoS), obtained from the Fourier transform of the velocity autocorrelation function, converges quickly, allowing the free energy, entropy, and other thermodynamic properties to be determined from short 20-ps MD trajectories. The anharmonic effects in the vibrations are accounted for by the broadening of the normal modes into bands from sampling the velocities over the trajectory. The low frequency diffusive modes, which lead to finite DoS at zero frequency, are accounted for by considering the DoS as a superposition of gas-phase and solid-phase components (two phases). The analytical decomposition of the DoS allows for an evaluation of properties contributed by different types of molecular motions. We show that this 2PT analysis leads to accurate predictions of entropy and energy of CO_2 over a wide range of conditions (from the triple point to the critical point of both the vapor and the liquid phases along the saturation line). This allows the equation of state of CO_2 to be determined, which is limited only by the accuracy of the force field. We also validated that the 2PT entropy agrees with that determined from thermodynamic integration, but 2PT requires only a fraction of the time. A complication for CO_2 is that its equilibrium configuration is linear, which would have only two rotational modes, but during the dynamics it is never exactly linear, so that there is a third mode from rotational about the axis. In this work, we show how to treat such linear molecules in the 2PT framework.
|Additional Information:||© 2011 American Chemical Society. Published In Issue June 14, 2011; Article ASAP May 25, 2011; Just Accepted Manuscript May 16, 2011; Received: March 27, 2011. This research was partially supported by the National Science Council of Taiwan (NSC 98-2221-E-002-087-MY3) and the Ministry of Economic Affairs of Taiwan (99-5226904000-04-04). The computation resources from the National Center for High-Performance Computing of Taiwan and the Computing and Information Networking Center of the National Taiwan University are acknowledged. W.A.G. acknowledges support from the WCU (World Class University) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (R31-2008-000-10055-0). W.A.G and T.A.P. acknowledge support from DOE (DE-FE0002057.DE-AC26-07NT42677, and DE-EE0003032).|
|Official Citation:||Absolute Entropy and Energy of Carbon Dioxide Using the Two-Phase Thermodynamic Model Shao-Nung Huang, Tod A. Pascal, William A. Goddard III, Prabal K. Maiti, Shiang-Tai Lin Journal of Chemical Theory and Computation 2011 7 (6), 1893-1901|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||28 Jun 2011 17:04|
|Last Modified:||26 Dec 2012 13:21|
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