Session W18: Theoretical Methods and Algorithms
2:30 PM–5:18 PM, Thursday, March 8, 2007
Colorado Convention Center Room: 103
Sponsoring Unit:
DCP
Chair: Anne Chaka, National Institute of Standards and Technology
Abstract ID: BAPS.2007.MAR.W18.9
Abstract: W18.00009 : Enthalpy of molecular solids beyond the harmonic approximation: application to hydrogen storage
4:06 PM–4:18 PM
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Abstract 
Authors:
Nikolai Zarkevich
D.D. Johnson
(Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St. Urbana, IL 68101.)
With low potential energy barriers, the harmonic approximation for phonon modes can be invalid [1]. Molecular solids are composed of strongly-bonded molecules held together by relatively weak intermolecular forces. As intermolecular interactions are usually not harmonic, a new theoretical approach is needed to obtain enthalpies of molecular solids at finite temperature. We develop such a theory for molecular solids and liquids, and apply it to obtain enthalpy differences between various phases from the first principles. We also calculate Gibbs free energy, and show that a phase diagram (e.g., a van't Hoff plot) can be constructed as a graphical solution of the Gibbs equation. To exemplify important applications, we consider materials and reactions for the high-capacity hydrogen storage. [1] Phys.Rev.Lett.97, 119601 (2006).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.MAR.W18.9