Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 144, Issue 12, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4944069
Keywords
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Funding
- U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials, Materials Science and Engineering Division
- Beatriu de Pinos program [BP-DGR 2011]
- US DOE by Iowa State University [DE-AC02-07CH11358]
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We investigate a general method to calculate the free energy of crystalline solids by considering the harmonic approximation and quasistatically switching the anharmonic contribution. The advantage of this method is that the harmonic approximation provides an already very accurate estimate of the free energy, and therefore the anharmonic term is numerically very small and can be determined to high accuracy. We further show that the anharmonic contribution to the free energy satisfies a number of exact inequalities that place constraints on its magnitude and allows approximate but fast and accurate estimates. The method is implemented into a readily available general software by combining the code HOODLT (Highly Optimized Object Oriented Dynamic Lattice Theory) for the harmonic part and the molecular dynamics (MD) simulation package HOOMD-blue for the anharmonic part. We use the method to calculate the low temperature phase diagram for Lennard-Jones particles. We demonstrate that hcp is the equilibrium phase at low temperature and pressure and obtain the coexistence curve with the fcc phase, which exhibits reentrant behavior. Several implications of the method are discussed. (C) 2016 AIP Publishing LLC.
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