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SUMMARY:Semi-stochastic and excited-state approaches in FCIQMC - Nicholas 
 Blunt (Chemistry)
DTSTART:20160610T110000Z
DTEND:20160610T114000Z
UID:TALK66102@talks.cam.ac.uk
CONTACT:Alex Thom
DESCRIPTION:FCIQMC is an approach introduced by Booth\, Thom and Alavi in 
 2009[1] to stochastically sample the solution of the Schrödinger equation
 \, and has since seen rapid algorithmic developments and many applications
 . In this talk we present two separate developments. Firstly\, we build on
  the semi-stochastic adaptation to FCIQMC introduced by Umrigar and co-wor
 kers[2]. In this\, the most important part of the projection is performed 
 exactly\, rather than stochastically\, thus resulting in reduced noise. We
  demonstrate the dramatic improvements that can occur with this approach f
 or a variety of systems\, both chemical and model in nature. Secondly\, we
  consider the calculation excited-state properties. This is initially done
  by analogy with the Lanczos algorithm\, subsequently allowing spectral an
 d finite-temperature properties to be calculated. Finding that this approa
 ch has some stability issues\, we consider a separate approach to sample i
 ndividual excited states\, and apply it to obtain highly accurate results 
 for the carbon dimer.\n\n[1] - 	G. H. Booth\, A. J. W. Thom\, and A. Alavi
 \, J. Chem. Phys. 131\, 054106 (2009)\n[2] - 	F. R. Petruzielo\, A. A. Hol
 mes\, H. J. Changlani\, M. P. Nightingale\, and C. J. Umrigar\, Phys. Rev.
  Lett. 109\, 230201 (2012)
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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