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SUMMARY:Dynamics from statics: A conceptual reformulation of Green’s fun
 ction perturbation theories - Oliver Backhouse\, Quantinuum
DTSTART:20250618T113000Z
DTEND:20250618T130000Z
UID:TALK230896@talks.cam.ac.uk
CONTACT:Chiara Leadbeater
DESCRIPTION:The use of the single-particle Green’s function in quantum c
 hemistry has become widespread as a result of its correspondence with the 
 spectral function\, allowing the study of a wide range of materials. I wil
 l present a method based on the block Lanczos approach that allows one to 
 determine a Lehmann representation of the fully dynamic Green's function\,
  and associated self-energy\, using only static expectation values in the 
 form of the spectral moments.\nThis recursion is\, in principle\, systemat
 ically improvable towards the limit of the fully dynamic functions\, howev
 er suffers from numerical instability in the context of floating point ari
 thmetic. Some results for classical quantum chemistry methods will show th
 at this does not limit the usefulness of the approach\, with acceptable er
 rors attainable with few iterations of the recursion.\nThe form of the mom
 ents of the Green's function offer opportunities for their calculation usi
 ng quantum algorithms\, and doing so introduces a simple hybrid quantum-cl
 assical algorithm sufficient to calculate Green's functions and self-energ
 ies on arbitrary quadrature.
LOCATION:Todd-Hamied Room\, Yusuf Hamied Department of Chemistry\, Cambrid
 ge
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