Assessment of Approximate Methods for Anharmonic Free Energies

• DOI: 10.1021/acs.jctc.9b00596
• Publication Date: 2019-09-18T21:17:44Z
• Authors: Venkat Kapil; Edgar Engel; Mariana Rossi; Michele Ceriotti
• Keywords: Condensed Matter - Materials Science; Statistical Mechanics (cond-mat.stat-mech); 0103 physical sciences; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; 01 natural sciences; Condensed Matter - Statistical Mechanics

Quantitative evaluation of the thermodynamic properties materials-most notably their stability, as measured by free energy-must take into account role thermal and zero-point energy fluctuations. While these effects can easily be estimated within a harmonic approximation, corrections arising from anharmonic nature interatomic potential are often crucial require computationally costly path integral simulations to obtain results that essentially exact for given potential. Consequently, different approximate frameworks computing affordable estimates energies have been developed over years. Understanding which approximations involved justified system, therefore choosing most suitable method, is complicated lack comparative benchmarks. To facilitate this choice we assess accuracy efficiency some commonly used methods: independent mode framework, vibrational self-consistent field, phonons. We compare correction Helmholtz against reference calculations. These benchmarks performed diverse set systems, ranging simple weakly solids flexible molecular crystals with freely rotating units. The suggest that, such allotropes carbon, methods yield in excellent agreement calculations, at considerably lower computational cost. For more complex systems polymorphs ice paracetamol do not consistently provide reliable approximation correction. Despite substantial cancellation errors when comparing stability phases, observe systematic improvement even relative energies. conclude least classes materials considered here, efforts toward obtaining feasible should directed reducing expense methods.