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Spin-Orbit and Spin-Spin Coupling in the Triplet State

The underlying theory of “Spin” of an electron and its associated inter-actions causing internal fields and spectral shift to bulk-magnetism iswell established now. Our understanding of spin properties is significant andmore useful than ever before. In recent years there seems to be an enormousinterest towards application oriented materials that harness those spin prop-erties. Theoretical simulations remain in a position to “assist or pilot” theexperimental discovery of new materials.In this work, we have outlined available methodologies for spin coupling inmulti-reference and DFT techniques. We have benchmarked multi-referencespin-Hamiltonian computation in isoelectronic diradicals - Trimethylenemethane(TMM) and Oxyallyl. Also with DFT, parameters are predicted with anewly discovered TMM-like stable diradicals, reported to have large positiveexchange interactions. Excellent agreement were obtained and our findingsemphasize that the dipole-dipole interactions alone can predict the splittingof triplet states and that DFT spin procedures hold well in organic species.We have extended our spin-studies to a highly application oriented ma-terial - nanographene. Using our novel spin-parameter arguments we haveexplained the magnetism of graphene. Our studies highlight a few signifi-cant aspects - first there seems to be a size dependency with respect to thespin-Hamiltonian; second, there is a negligible contribution of spin-orbit cou-pling in these systems; third, we give a theoretical account of spin restrictedand unrestricted schemes for the DFT method and their consequences forthe spin and spatial symmetry of the molecules; and, finally, we highlightthe importance of impurities and defects for magnetism in graphene. Wepredict triplet-singlet transitions through linear response TDDFT for thetris(8-hydroxyquinoline) aluminium complex, an organic molecule shown tohave spintronics applications in recent experiments. Our spin studies werein line with those observations and could help to understand the role of thespin-coupling phenomena. / QC 20120531

Identiferoai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-95761
Date January 2012
CreatorsPerumal, Sathya Sai Ramakrishna Raj
PublisherKTH, Teoretisk kemi och biologi, Stockholm
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text
Formatapplication/pdf
Rightsinfo:eu-repo/semantics/openAccess
RelationTrita-BIO-Report, 1654-2312 ; 2012:17

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