Tamukong, Patrick K.
Extension and applications of the GVVPT2 method to the study of transition metals.
Degree: PhD, Chemistry, 2014, University of North Dakota
The ground and low-lying excited electronic states of molecules of the first ( 2 Sc , 2 Cr , 2 Mn , and 2 Ni ) and second ( 2 Y , 2 Mo , and 2 Tc ) row of transition elements have been investigated for the first time with the generalized Van Vleck second order multireference perturbation theory (GVVPT2) method, a variant of MRPT. All potential energy curves (PECs) obtained in these studies were smooth and continuous; that is, they are free from wiggles or inflexion points. In order to account for relativistic effects, which become important in heavy elements, the GVVPT2 method was extended to include scalar relativistic effects through the spin-free exact two component (sf-X2C) method and used in the studies of all molecules of second row transition elements and some of those of the first row considered in this present work. GVVPT2 studies of triatomic lithium and beryllium were also done as a first step to studies of small clusters of transition metals. The spectroscopic constants (bond lengths, harmonic frequencies, bond energies, and adiabatic transition energies) obtained for all PECs at the GVVPT2 level were in good agreement with experimental data, where available, and with results from previous studies using other high level ab initio methods. Optimized geometries of the triatomics were also in good agreement with previous findings. The studies included electronic states (e.g., the g 1 g 1 2 Σ and 3 Σ states of 2 Y as well as the g 5 1 Σ and g 9 1 Σ states of 2 Tc ) not previously discussed in the literature.
As a first step to applying GVVPT2 to the study of relatively larger systems, the present work includes the results of efforts on improving DFT-in-DFT embedding theory. New equations were determined which involved an additional constraint of orthogonality of the orbitals of one subsystem to those of the complementary subsystem as warranted by formal arguments based on the formulation of DFT-in-DFT embedding. A computer program was realized using the new embedding equations and test calculations performed. Analyses of electron density deformations in embedding theory, in comparison with conventional Kohn-Sham (KS)-DFT densities, were performed using the new embedding program and a computer code that was also written to compute electron densities of molecules in real space, given reduced one particle density matrices. The results revealed that whereas the current formulation of DFT-in-DFT embedding theory generally underestimates electron density, at the interface between subsystems in comparison with conventional KS-DFT calculations of the supermolecule, the new DFT-in-DFT embedding scheme with the external orthogonality constraint was found to remedy the situation. Worthy of special note in this new embedding protocol is the fact that the nonadditive kinetic potential ( T v ), thought to be a major cause of weaknesses in DFT-in-DFT embedding and to which many previous research efforts have been devoted, can be set exactly to zero. The present work therefore realized, for the first time,…
Advisors/Committee Members: Dr. Mark R. Hoffmann, Dr. Harmon Abrahamson, Dr. Kathryn Thomasson.
Subjects/Keywords: perturbation (mathematics); transition metals; Chemistry
to Zotero / EndNote / Reference
APA (6th Edition):
Tamukong, P. K. (2014). Extension and applications of the GVVPT2 method to the study of transition metals. (Doctoral Dissertation). University of North Dakota. Retrieved from https://commons.und.edu/theses/573
Chicago Manual of Style (16th Edition):
Tamukong, Patrick K. “Extension and applications of the GVVPT2 method to the study of transition metals.” 2014. Doctoral Dissertation, University of North Dakota. Accessed April 11, 2021.
MLA Handbook (7th Edition):
Tamukong, Patrick K. “Extension and applications of the GVVPT2 method to the study of transition metals.” 2014. Web. 11 Apr 2021.
Tamukong PK. Extension and applications of the GVVPT2 method to the study of transition metals. [Internet] [Doctoral dissertation]. University of North Dakota; 2014. [cited 2021 Apr 11].
Available from: https://commons.und.edu/theses/573.
Council of Science Editors:
Tamukong PK. Extension and applications of the GVVPT2 method to the study of transition metals. [Doctoral Dissertation]. University of North Dakota; 2014. Available from: https://commons.und.edu/theses/573