Universität zu Köln

Zhang, Jun (2015). Incremental Scheme: A General Approach For Electron Correlation Computations of Large Molecules. PhD thesis, Universität zu Köln.

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Abstract

The first part of this work introduces incremental scheme as a general approach for electron correlation computations of large molecules, especially its latest implementation: third-order incremental dual-basis set zero buffer (inc3-db-B0) approach. This approach can combine with CCSD, CCSD(T) and their explicit correlation variants to obtain accurate correlation energies in a highly efficient way, and is presented in detail in this work. A program Apts has be developed for a black-box and automatic implementation of these methods. With various strategies, the inc3-db-B0 approach can reduce the wall time of a calculation of a large molecule by up to 10 times, and the error in absolute and especially relative energies can be less than 1 kcal mol$^{-1}$, making it a reliable method for the treatment of energetically nearly degenerate isomers of large molecules and other kinds of chemical species. A series of applications of the inc3-db-B0 approach in many real chemical problems are then described, including: benchmark set validation; energies of isomers of water clusters; the rotational barrier of biphenyl; hydration of lanthanide trivalent ions; the relative stability of isomers of double fullerene adducts; singlet-triplet gap of biphenylcarbene, and vertical detachment energy of green fluorescent protein chromophore. These problems involve both inorganic and organic chemistry, closed-shell and open-shell molecules. The inc3-db-B0 approach exhibits excellent performance in various kinds of chemical problems, confirming it a promising method for general chemical problems. Finally, the potential direction of further extension of incremental scheme is discussed. The second part of this work introduces the idea of labile capping bond phenomenon. For a wide range of trivalent lanthanide ion coordination complexes of tricapped trigonal prism or monocapped square antiprism configurations, the bonds between the central lanthanide ions and the capping ligands are found to violate Badger's rule: they can get weaker as they get shorter. We demonstrate that this observation originates from the screening and repulsion effect of the prism ligands. Both effects enhance as the electric field of the central ion or the softness of the prism ligands increases. Thus for heavier lanthanides despite that the capping bond could be shorter, it is more efficient to be weakened by the prism ligands, being inherently labile. This concept of "labile capping bonds" has been successfully used to interpret many experiments, especially we have built an elegant model to solve a problem in the water exchange kinetics of lanthanide ions that has puzzled investigators for a long time: why the exchange rate reaches a maximum for the middle region, but is low at the beginning and end of the lanthanide series. We also use it to interpret why the twistted square antiprism isomer of some lanthanide complexes exhibits much higher water exchange rate than the square antiprism isomer does. We believe that the labile capping bond phenomenon can offer new insights in understanding chemical problems.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Zhang, Jun zhangjunqcc@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-60755
Date:	12 April 2015
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Theoretical Chemistry
Subjects:	Natural sciences and mathematics Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language Incremental scheme English Large molecule English quantum chemistry English Labile capping bond English UNSPECIFIED English
Date of oral exam:	15 January 2015
Referee:	Name Academic Title Dolg, Michael Prof. Dr. Hanrath, Michael PD. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/6075