Towards a new implementation of 'MREOM-CC’, with application to MO+ dimers (M = V, Cr, Mn, Fe, Co, Ni)

Coupled-Cluster Theory;Excited States;Multi Reference;Transition Metals

Steffen, Johnathanaffiliation1:Faculty of Science ; advisor:Nooijen, Marcel ; advisor:Hopkins, W. Scott ; Nooijen, Marcel ; Hopkins, W. Scott ;

University of Waterloo

关键词: Coupled-Cluster Theory;    Excited States;    Master Thesis;    Transition Metals;    Multi Reference;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/12955/1/Steffen_Johnathan.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

MultiReferenceEquationofMotionCoupledCluster(MREOM-CC)isanelectronicstructure methodthatallowsthe calculationofmanyelectronicstatessimultaneously.Asequenceof transformations are applied to a Hamiltonian allowing for a subsequent diagonalization of a much smaller subspace. These transformations preserve the eigenvalues of the original Hamiltonian, and paradoxically calculations increasein accuracy while simultaneously reducingthe cost of the calculation. MREOM has previously been used to calculate transition metal atom spectra as well as vertical excitation spectra from organic molecules and transition metal complexes. Inthisthesis,MREOMisusedtocalculateapotentialenergysurfaceforseveralsystems containingmanyexcitedstates.Thesystemsstudiedinthisthesisarepositivelychargeddiatomic transition metal oxides (MO+, M = V, Cr, Mn, Fe, Co, Ni)chosen for both their electronic complexity as well as the opportunity for a tandem experimental study in the Hopkins lab. Calculations were approached using either a high spin or low spin regime for the reference states of each system. High spin systems convergedathighinteratomicdistancebutgenerallyexhibiteddiscontinuities.Lowspinsystems appearedsmoothbutweretroublesometosetup.However,MREOMisnotrecommendedfor complicated potential energy surfaces until further improvements can be made.Inasecondprojectanimprovedalgorithmisdevelopedforthetime-consumingfinal diagonalization step in MREOM. Using acarefully designed data structure for multiple electronic states the critical multiplication of ;; ∙ ” is carried out efficiently, with minimal resorting and efficient BLAS matrix-matrix multiplication steps. The implementation is not yet complete, and requires interfacing with the rest of the code.