Natural orbitals for many-body expansion methods

Abstract An Approximation of Löwdin's Natural Orbitals for Molecules with a Green's Function Method The many-body-pertubation theorie of the single-particle Green's function is used to get an approximate first-order density matrix. Slightly modified SCF-orbitals form the basis for the expansion. The mass-operator in Dyson's equation is considered up to second order in the Perturbation. In the present form the method is only applicable to ground states with closed shells. The ground states of the molecules LiH and NH3 serve as examples to demonstrate the usefulness of the directly calculated natural orbitals for application in the C I-method. The natural orbitals give a much better convergence of the C I-expansion than the SCF-orbitals do.

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Direct Calculation of Natural Orbitals by Many‐Body Perturbation Theory: Application to Helium

The Journal of Chemical Physics ◽

10.1063/1.1671446 ◽

1969 ◽

Vol 50 (6) ◽

pp. 2767-2768 ◽

Cited By ~ 65

Author(s):

William P. Reinhardt ◽

Jimmie D. Doll

Keyword(s):

Perturbation Theory ◽

Direct Calculation ◽

Many Body ◽

Natural Orbitals ◽

Theory Application ◽

Many Body Perturbation Theory

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Many-body calculations of the hyperfine interaction of some excited states of alkali atoms, using approximate Brueckner or natural orbitals

Zeitschrift für Physik A Atoms and Nuclei ◽

10.1007/bf01437866 ◽

1976 ◽

Vol 279 (2) ◽

pp. 113-125 ◽

Cited By ~ 101

Author(s):

Ingvar Lindgren ◽

Johannes Lindgren ◽

Ann-Marie M�rtensson

Keyword(s):

Hyperfine Interaction ◽

Excited States ◽

Many Body ◽

Natural Orbitals ◽

Alkali Atoms

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Approximate natural orbitals and the convergence of a second order multireference many‐body perturbation theory (CIPSI) algorithm

The Journal of Chemical Physics ◽

10.1063/1.455405 ◽

1988 ◽

Vol 89 (10) ◽

pp. 6376-6384 ◽

Cited By ~ 39

Author(s):

F. Illas ◽

J. Rubio ◽

J. M. Ricart

Keyword(s):

Perturbation Theory ◽

Second Order ◽

Many Body ◽

Natural Orbitals ◽

Many Body Perturbation Theory

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Many-body localization in the Fock space of natural orbitals

SciPost Physics ◽

10.21468/scipostphys.4.6.038 ◽

2018 ◽

Vol 4 (6) ◽

Cited By ~ 2

Author(s):

Wouter Buijsman ◽

Vladimir Gritsev ◽

Vadim Cheianov

Keyword(s):

Fock Space ◽

Disorder Strength ◽

Many Body ◽

Natural Orbitals ◽

Localization Transition ◽

Participation Ratio ◽

The Many ◽

Computational Basis

We study the eigenstates of a paradigmatic model of many-body localization in the Fock basis constructed out of the natural orbitals. By numerically studying the participation ratio, we identify a sharp crossover between different phases at a disorder strength close to the disorder strength at which subdiffusive behaviour sets in, significantly below the many-body localization transition. We repeat the analysis in the conventionally used computational basis, and show that many-body localized eigenstates are much stronger localized in the Fock basis constructed out of the natural orbitals than in the computational basis.

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