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SUMMARY:Assessment of Approximate Methods for Anharmonic Free Energies - V
 enkat Kapil\, EPFL
DTSTART:20200217T141500Z
DTEND:20200217T151500Z
UID:TALK138943@talks.cam.ac.uk
CONTACT:Bartomeu Monserrat
DESCRIPTION:Quantitative estimations of thermodynamic stabilities – meas
 ured by free energies – must take into account thermal and zero-point en
 ergy fluctuations. While these effects are easily estimated within a harmo
 nic approximation\, corrections arising from the anharmonic nature of the 
 interatomic potential are often crucial and require expensive path integra
 l simulations. Consequently\, different approximate methods for computing 
 affordable estimates of anharmonic free energies have been developed. Unde
 rstanding which of the approximations involved are justified for a given s
 ystem is complicated by the lack of comparative benchmarks. To facilitate 
 this choice we assess the ac- curacy of some of the commonly used approxim
 ate methods: vibrational self-consistent field and self-consistent phonons
 . We compare anharmonic corrections to Helmholtz free energies against ref
 - erence path integral calculations for a diverse set of systems\, ranging
  from simple weakly anharmonic solids to flexible molecular crystals with 
 freely-rotating units [1]. We conclude that efforts towards obtaining comp
 utationally-feasible anharmonic free-energies of molecular systems should 
 be directed towards reducing the expense of path integral methods\, while 
 the approximate methods should be used as an effective sampling approach t
 o generate data to train and validate machine learning potentials that giv
 e access to highly accurate and low cost ab initio interatomic interaction
 s.\n\n[1] Venkat Kapil\, Edgar Engel\, Mariana Rossi\, and Michele Ceriott
 i. Assessment of Approxi- mate Methods for Anharmonic Free Energies. Journ
 al of Chemical Theory and Computation\, 15(11):5845–5857\, November 2019
 .
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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