Classical and quantum calculations of the temperature dependence of the free energy of argon
File(s)
Accepted version
Author(s)
Xu, W
Horsfield, AP
Wearing, D
Lee, P
Type
Journal Article
Abstract
The free energy is central to statistical mechanics and thermodynamics, and its accurate calculation via. computational modelling is important for a large number of applications, especially when its experimental value is hard to obtain. Several established and general methods for calculating the Helmholtz free energy across different length scales, including continuum, atomistic and quantum mechanical, are compared and analyzed. A computational approach is then proposed to calculate the temperature dependences of internal energy and absolute Helmholtz free energy for solid and liquid phases with the coupling of thermodynamic integration (TI) and harmonic approximation calculations from both classical molecular dynamics (MD) and density functional theory (DFT). We use the Lennard-Jones system as an example (i.e. argon) for the demonstration of the approach. It is observed that the free energy transits smoothly from being describable by the harmonic approximation to including anharmonic effects at a transition temperature around 0.56 Tm; below this temperature, the quantum behavior of atoms is important. At higher temperatures (T > 0.56 Tm), the TI and harmonic approximation results for the Helmholtz free energy functions become increasingly divergent with the increase of temperature. This work demonstrates that a multiscale approach employing TI, MD, and DFT can provide accurate calculations of the temperature dependence of absolute Helmholtz free energy for both solid and liquid phases.
Date Issued
2017-12-11
Date Acceptance
2017-12-01
Citation
Computational Materials Science, 2017, 144, pp.36-41
ISSN
0927-0256
Publisher
Elsevier
Start Page
36
End Page
41
Journal / Book Title
Computational Materials Science
Volume
144
Copyright Statement
© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/
Subjects
0912 Materials Engineering
0204 Condensed Matter Physics
Materials
Publication Status
Published