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Open‐shell systems investigated with Monte Carlo configuration interaction
Author(s) -
Coe J. P.,
Paterson M. J.
Publication year - 2016
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.25222
Subject(s) - wave function , configuration interaction , open shell , monte carlo method , slater determinant , quantum monte carlo , full configuration interaction , atomic orbital , statistical physics , physics , chemistry , quantum mechanics , electron , molecule , mathematics , statistics
We investigate the open‐shell systems of the methyl radical, the allyl radical and molecular oxygen using Monte Carlo configuration interaction. We look at whether modifying Monte Carlo configuration interaction to use the increased flexibility of unrestricted Hartree‐Fock orbitals offers any benefits in the description of these systems by the resulting compact wavefunctions. The expectation of the total spin squared when using Slater determinants is calculated to investigate if pure spin states can be evolved by Monte Carlo configuration interaction and how this might be accelerated. We consider the multireference character of these open‐shell systems. To this end we demonstrate how a previously introduced way [J. P. Coe and M. J. Paterson, J. Chem. Theory Comput. 11, 4189 (2015)] of viewing a multireference indicator of P.‐O. Löwdin [P.‐O. Löwdin, Phys. Rev. 97, 1474 (1955)] in terms of the spatial entanglement can be generalized to open‐shell systems.