The computationally expensive evaluation and storage of high-rank reduced density matrices (RDMs) has been the bottleneck in the calculation of dynamic correlation for multireference wave functions in large active spaces. We present a stochastic formulation of multireference configuration interaction and perturbation theory that avoids the need for these expensive RDMs. The algorithm presented here is flexible enough to incorporate a wide variety of active space reference wave functions, including selected configuration interaction, matrix product states, and symmetry-projected Jastrow mean field wave functions. It enjoys the usual attractive features of Monte Carlo methods, such as embarrassing parallelizability and low memory costs. We find that the stochastic algorithm is already competitive with the deterministic algorithm for small active spaces, containing as few as 14 orbitals. We illustrate the utility of our stochastic formulation using benchmark applications.
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Multireference configuration interaction and perturbation theory without
reduced density matrices
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7 December 2019
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December 02 2019
Multireference configuration interaction and perturbation theory without
reduced density matrices

Special Collection:
JCP Emerging Investigators Special Collection
Ankit Mahajan
;
Ankit Mahajan
1
Department of Chemistry, University of
Colorado
, Boulder, Colorado 80302, USA
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Nick S. Blunt
;
Nick S. Blunt
2
Department of Chemistry
, Lensfield
Road, Cambridge CB2 1EW, United Kingdom
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Iliya Sabzevari
;
Iliya Sabzevari
1
Department of Chemistry, University of
Colorado
, Boulder, Colorado 80302, USA
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Sandeep Sharma
Sandeep Sharma
a)
1
Department of Chemistry, University of
Colorado
, Boulder, Colorado 80302, USA
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J. Chem. Phys. 151, 211102 (2019)
Article history
Received:
September 16 2019
Accepted:
November 07 2019
Connected Content
A companion article has been published:
Stochastic approach optimizes a system’s wavefunction to improve computational efficiency
Citation
Ankit Mahajan, Nick S. Blunt, Iliya Sabzevari, Sandeep Sharma; Multireference configuration interaction and perturbation theory without reduced density matrices. J. Chem. Phys. 7 December 2019; 151 (21): 211102. https://doi.org/10.1063/1.5128115
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