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CATEGORIES:Theory - Chemistry Research Interest Group
SUMMARY:Approaching Exact Quantum Chemistry by Stochastic
Wave Function Sampling and Deterministic Coupled-C
luster Computations - Professor Piotr Piecuch\, M
ichigan State University
DTSTART;TZID=Europe/London:20200304T141500
DTEND;TZID=Europe/London:20200304T151500
UID:TALK127531AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/127531
DESCRIPTION:One of the main goals of electronic structure theo
ry is to precisely describe increasingly complex p
olyatomic systems. It is widely accepted that size
extensive methods based on the exponential wave f
unction ansatz of coupled-cluster (CC) theory and
their extensions to excited states via the equatio
n-of-motion (EOM) formalism are excellent candidat
es for addressing this goal. In this talk\, I will
discuss a radically new way of obtaining accurate
energetics equivalent to high-level CC calculatio
ns\, such as CCSDT or CCSDTQ\, at a small fraction
of the computational cost\, even when multirefere
nce correlation effects become significant\, resul
ting from the merger of a deterministic formalism\
, abbreviated as CC(P\;Q) [1\,2]\, with the stocha
stic CI [3\,4] and CC [5] Quantum Monte Carlo (QMC
) approaches [6]. I will also demonstrate that one
can take the merger of stochastic and determinist
ic ideas to the ultimate level and use it to extra
ct the exact\, full CI (FCI)\, energetics out of t
he early stages of FCIQMC propagations with the he
lp of the relatively inexpensive polynomial steps
similar to CCSD calculations\, eliminating exponen
tial complexity of conventional FCI Hamiltonian di
agonalizations altogether [7]. The advantages of t
he new methodologies will be illustrated by molecu
lar examples\, where the goal is to recover the ne
arly exact\, CCSDT and CCSDTQ\, and exact\, FCI\,
energetics in situations involving chemical bond d
issociations and reaction pathways and many-electr
on systems beyond the reach of FCI. Extensions to
excited electronic states by a combination of stoc
hastic CIQMC and deterministic EOMCC computations
[8] and converging FCI energetics in strongly corr
elated systems\, such as those involved in modelin
g metalâ€“insulator transitions [9]\, where the trad
itional CCSD\, CCSDT\, CCSDTQ\, etc. hierarchy bre
aks down\, will be discussed as well.\n\nReference
s\n[1] J. Shen and P. Piecuch\, Chem. Phys. 401\,
180 (2012)\; J. Chem. Phys. 136\, 144104 (2012).\n
[2] N. P. Bauman\, J. Shen\, and P. Piecuch\, Mol.
Phys. 115\, 2860 (2017).\n[3] G. H. Booth\, A. J.
W. Thom\, and A. Alavi\, J. Chem. Phys. 131\, 054
106 (2009).\n[4] D. Cleland\, G. H. Booth\, and A.
Alavi\, J. Chem. Phys. 132\, 041103 (2010).\n[5]
A. J. W. Thom\, Phys. Rev. Lett. 105\, 263004 (201
0).\n[6] J. E. Deustua\, J. Shen\, and P. Piecuch\
, Phys. Rev. Lett. 119\, 223003 (2017)\; in prepar
ation.\n[7] J. E. Deustua\, I. Magoulas\, J. Shen\
, and P. Piecuch\, J. Chem. Phys. 149\, 151101 (20
18).\n[8] J. E. Deustua\, S. H. Yuwono\, J. Shen\,
and P. Piecuch\, J. Chem. Phys. 150\, 111101 (201
9)\; S. H. Yuwono\, A. Chakraborty\, J. E. Deustua
\, J. Shen\, and P. Piecuch\, in preparation.\n[9]
I. Magoulas\, J. E. Deustua\, J. Shen\, and P. Pi
ecuch\, in preparation.\n
LOCATION:Department of Chemistry\, Cambridge\, Unilever lec
ture theatre
CONTACT:Lisa Masters
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