Hybrid Correlation Models For Bond Breaking Based On Active Space Partitioning

Nuclear orbitals;Lowdin's partitioning technique;Goldstone diagrammatic technique;Coupled cluster theory;Moller-Plesset perturbation theory;Bond breaking

Bochevarov, Artem D. ; Chemistry and Biochemistry

University:Georgia Institute of Technology

Department:Chemistry and Biochemistry

关键词: Nuclear orbitals;    Lowdin's partitioning technique;    Goldstone diagrammatic technique;    Coupled cluster theory;    Moller-Plesset perturbation theory;    Bond breaking;   

Others  :  https://smartech.gatech.edu/bitstream/1853/11593/1/bochevarov_artem_d_200608_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

The work presented in this thesis is dedicated to developing inexpensive quantum-chemical models that are able to produce smooth and physically correct potential energy curves for thedissociation of single covalent bonds. It is well known that the energies produced by many ab initio theories scaling as the fifth order with the system size (for instance, second-orderMoller-Plesset (MP2) and Epstein-Nesbet perturbation theories) diverge at large interatomic separations. We show that thedivergent behavior of such perturbation schemes is due to a small number of terms in the energy expressions. Then, we demonstrate that the self-consistent replacement of these terms by theiranalogs from the coupled cluster theory (such as CCSD) allows one to redress the erroneous behavior of the perturbation theorieswithout the damage to the overall scaling.We also investigate the accuracy of these hybrid perturbation theory-coupled cluster theories near equilibrium geometry. Judging from the computed spectroscopic constants and shapes of the potential energy curves, one such model, denotedMP2-CCSD(II) in this work, performs consistently better than the MP2 theory at essentially the same computational cost.