Investigating Multireference Character and Correlation in Quantum Chemistry

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Abstract

We review a range of multireference diagnostics for quantum chemistry and discuss them in terms of choices of the molecular orbitals. We show how an approach<sup>1</sup> of P.-O. Löwdin can also be viewed as quantifying the electron correlation via the spatial entanglement relative to a single determinant. We consider three example systems from quantum chemistry that exhibit three different combinations of multireference character and correlation: not strongly multireference and not strongly correlated, strongly multireference but not strongly correlated, and strongly multireference together with strong correlation. We find that a multireference measure (MR) does not change substantially with the cutoff used for a Monte Carlo configuration interaction calculation and investigate the effect of using natural orbitals. We see that a coupled-cluster singles and doubles diagnostic and a density-functional theory diagnostic give a correct general prediction of the multireference character for these systems. We also look at the issue of multireference character for a collection of noninteracting hydrogen molecules and the effect of basis size on the multireference character of a stretched hydrogen molecule. (Graph Presented).

Original languageEnglish
Pages (from-to)4189-4196
Number of pages8
JournalJournal of Chemical Theory and Computation
Volume11
Issue number9
Early online date10 Aug 2015
DOIs
Publication statusPublished - 8 Sep 2015

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Computer Science Applications

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