BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Path integral molecular dynamics for indistinguishable particles -
  Barak Hirshberg\, Tel Aviv University
DTSTART:20220224T140000Z
DTEND:20220224T150000Z
UID:TALK166345@talks.cam.ac.uk
CONTACT:Edgar Engel
DESCRIPTION:Whether particles are bosons or fermions is a most fundamental
  property of quantum- mechanical systems. It is particularly important for
  accurately describing\, for example\, ultracold trapped atoms\, electrons
  in quantum dots and nuclear spin isomers of hydrogen. Path integral molec
 ular dynamics (PIMD) simulations are widely used to study quantum effects 
 in chemistry and physics. However\, they completely neglect this property 
 assuming the particles are distinguishable.\n\nWe present a new method for
  simulating indistinguishable particles using PIMD. For bosons\, the main 
 difficulty is enumerating all particle permutations\, which scales exponen
 tially with system size. We show that the potential and forces can be eval
 uated using a recurrence relation that avoids enumerating all permutations
  while providing the correct thermal expectation values. The resulting alg
 orithm reduces the scaling from exponential to cubic\, allowing the first 
 applications of PIMD to large bosonic systems [1].\n\nFor fermions\, the i
 nfamous sign problem presents an additional formidable challenge\, limitin
 g applications to moderate temperatures and strongly-repelling systems. By
  harnessing the power of free-energy methods\, we are able to alleviate th
 e sign problem and study small systems at temperatures three times lower t
 han using standard PIMD [2-3].\n\nApplications ranging from models of ultr
 acold trapped atoms [1] and electrons in two-dimensional quantum dots [2-3
 ] to a supersolid phase of deuterium under high-pressure and low temperatu
 re [4] will be discussed. I will also present an analysis of the condensat
 e fraction and the role of exchange effects at different temperatures\, th
 rough the relative probability of different ring-polymer configurations.\n
 \nReferences\n1. B. Hirshberg\, V. Rizzi and M. Parrinello\, Proc. Natl. A
 cad. Sci. USA (2019) 116 21445-21449.\n2. B. Hirshberg\, M. Invernizzi and
  M. Parrinello\, J. Chem. Phys. (2020) 152\, 171102. \n3. T. Dornheim\, M.
  Invernizzi\, J. Vorberger and B. Hirshberg\, J. Chem. Phys. (2020) 153\, 
 234104.\n4. C.W. Myung\, B. Hirshberg\, and M. Parrinello Phys. Rev. Lett.
  (2022) 128\, 045301.
LOCATION:TCM Seminar room\, 530 Mott building
END:VEVENT
END:VCALENDAR