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UBC Theses and Dissertations

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UBC Theses and Dissertations

Population analyses based on ionic partition of overlap distribution Wang, Yiming


In this thesis, we bring up several new schemes of partitioning the atomic partial charges for the purpose of reducing the dependency on the basis sets and the inaccuracy from previous methods we did in our group. We analyze all the methods including Mulliken, evaluate them by comparing with Natu- ral Population Analysis (NPA) with several different groups of systems which we divide according to their polarity. We find that when applied to more polarized systems such as compounds containing Fluorine, our Population Analyses Based on Ionic Partition of Overlap Distributions (IPOD) series perform better and produce charges closer to those of NPA method. Within the same system, IPOD series work better for atoms with more polarized bond than for atoms with non-polarized ones. On top of all the analyses for separate groups, we plot the correlation between charges produced by different methods with charges generated by NPA method. From the graph and the slope value we conclude that IPOD2d is the method which gives the most reliable result compared to NPA among all the methods. Also, in order to figure out the best basis set which can represent the result of IPOD2d, we plot the correlation graph between charges produced by IPOD2d and NPA methods for several basis sets. We find that 6-31G basis set is the most representative basis set. Using the 6-31G to calculate charges for certain systems renders us lots of advantages in terms of computational efficiency while still providing a reasonable result.

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