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The Triplet-Singlet Gap in the m-Xylylene Radical: A Not So Simple One

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Title The Triplet-Singlet Gap in the m-Xylylene Radical: A Not So Simple One
 
Creator MANERU, DR
PAL, AK
MOREIRA, IDR
DATTA, SN
ILLAS, F
 
Subject INTRAMOLECULAR FERROMAGNETIC INTERACTION
DENSITY-FUNCTIONAL THEORY
MOLECULAR-ORBITAL METHODS
PHENYLENE COUPLING UNIT
PLESSET PERTURBATION TREATMENT
MAIN-GROUP THERMOCHEMISTRY
TRANSITION-METAL DIMERS
SELF-CONSISTENT-FIELD
COMPLETE ACTIVE SPACE
REFERENCED KOHN-SHAM
 
Description Meta-benzoquinodimethane (MBQDM) or m-xylylene provides a model for larger organic diradicals, the triplet-singlet gap being the key property. In the present work this energy difference has been the object of a systematic study by means of several density functional theory-based methods including B3LYP, M06, M06-2X, HSE and LC-omega PBE potentials and a variety of wave function-based methods such as complete active space self consistent field (CASSCF), Multireference second-order Moller-Plesset (MRMP), difference dedicated configuration interaction (DDCI), and Multireference configuration interaction (MRCI). In each case various basis sets of increasing quality have been explored, and the effect of the molecular geometry is also analyzed. The use of the triplet and broken symmetry (BS) solutions for the corresponding optimized geometries obtained from B3LYP and especially M06-2X functionals provide the value of the adiabatic triplet-singlet gap closer to experiment when compared to the reported value of Wenthold, Kim, and Lineberger, (J. Am. Chem. Soc. 1997, 119, 1354) and also for the electron affinity. The agreement further improves using the full pi-valence CASSCF(8,8) optimized geometry as an attempt to correct for the spin contamination effects on the geometry of the BS state. The CASSCF, MRMP, and MRCI, even with the full pi valence CAS(8,8) as reference and relatively large basis set, systematically overestimate the experimental value indicating either that an accurate description must go beyond this level of theory, including a electrons and higher order polarization functions, or perhaps that the measured value is affected by the experimental conditions.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-12-28T13:11:41Z
2014-12-28T13:11:41Z
2014
 
Type Article
 
Identifier JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 10(1)335-345
1549-9618
1549-9626
http://dx.doi.org/10.1021/ct400883m
http://dspace.library.iitb.ac.in/jspui/handle/100/16683
 
Language English