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Stochastic Coupled Cluster Theory Alex J. W. Thom

Summary: Stochastic Coupled Cluster Theory
Alex J. W. Thom
Department of Chemistry, Imperial College London, London SW7 2AZ, U.K. and
University of Cambridge, Chemistry Department, Lensfield Road, Cambridge CB2 1EW, U.K.
(Dated: December 4, 2010)
We describe a Stochastic Coupled Cluster Theory which represents excitation amplitudes as dis-
crete excitors in the space of excitation amplitudes. Re-expressing the Coupled Cluster (CC) equa-
tions as the dynamics of `excitors' in this space, we show that a simple set of rules suffice to evolve
a distribution of excitors to sample the CC solution and correctly evaluate the CC energy. These
rules are not truncation-specific and this method can calculate CC solutions to an arbitrary level of
truncation. We present results of calculation on the neon atom, and nitrogen and water molecules
showing the ability to recover both truncated and full CC results.
Coupled Cluster Theory has been said to be the gold-
standard of electronic structure methods, and is routinely
used in many branches of physics[13]. With the addition
of perturbatitive corrections, CCSD(T) can routinely
produce energies well within `chemical accuracy'[4], of
1 kcal/mol. It has the desirable property that trunca-
tions of the theory are size extensive and rapidly con-
verge with increasing truncation level to give spectro-


Source: Alavi, Ali - Department of Chemistry, University of Cambridge


Collections: Chemistry