Pastore, Mariachiara (2009) Multireference Perturbation Theories for the accurate calculation of energy and molecular properties. PhD Thesis , Università degli studi di Ferrara.

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Abstract
This Ph.D. thesis deals with the development and the applications of NElectron Valence State Perturbation Theory (NEVPT), a novel form of Multireference Perturbation Theory (MRPT) put forward in collaboration between the theoretical chemistry groups of the uni versities of Ferrara and Toulouse. A review of the NEVPT approach is presented, starting from the original second order state–specific formulation, going through the quasidegenerate multi–state extension and arriving at the implementations of the third order in the energy and of the internally contracted configuration interaction, accomplished during the Ph.D. The chief properties of NEVPT are analyzed and the test case of the C2 molecule is discussed. An important field of applications of MRPTs is the calculation of the electronically excited states of molecules, where the strong differential correlation effects and the possible multiref erence nature of the wavefunctions can be, in principle, successfully handled by a “variational plus perturbation” scheme. Concerning the applications, the thesis is divided in two parts. Part I concerns the calculation of electronically excited states. Different issues are addressed: on the one hand the treatment of small aromatic molecules, Pyrrole, Furan and Thiophene, whose description is complicated by the possible interaction with lowlying Rydberg states and by the ionic nature of some valence states, extremely sensitive to the socalled dynamical − polarization; on the other hand the case of a largesized aromatic molecule, FreeBase Por phin, for which the crucial problem is the choice of a balanced variational space to accurately describe the wavefunctions of the ground and of the excited states. The second part is devoted to the description, by means of MRPT, of the Electron Transfer (ET) process in MixedValence systems. The investigation is carried out on a model spiro − − compound, for which the ET reaction is simulated using a simplified onemode twostate model. The inadequacy of a standard second order MRPT approach is shown and the application of an alternative and effective computational strategy is discussed.
Item Type:  Thesis (PhD Thesis) 

Date:  13 March 2009 
Tutor:  Cimiraglia, Renzo 
Coordinator:  Gilli, Gastone 
Institution:  Università degli studi di Ferrara 
PhD:  XXI Anno 2006 > SCIENZE CHIMICHE 
Divisions:  Dipartimento > Chimica 
Subjects:  Area 03  Scienze chimiche > CHIM/02 Chimica fisica 
Uncontrolled Keywords:  computational chemistry, perturbation theory, excited states 
Deposited on:  05 Jul 2009 15:36 
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