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dc.contributor.authorWorsnop, Stephen Kent.en_US
dc.date.accessioned2014-10-21T12:35:48Z
dc.date.available2014-10-21T12:35:48Z
dc.date.issued1999en_US
dc.identifier.otherAAINQ49300en_US
dc.identifier.urihttp://hdl.handle.net/10222/55683
dc.descriptionThe accuracy of electron densities calculated using density functional theory (DFT) is assessed by comparison with results obtained from conventional ab initio methods based upon the Hartree-Fock (HF) ground state wavefunction. To simplify the comparisons new methods are introduced and are combined with other established tools. The information gained with these various methods is then used to determine parameters for two hybrid functionals.en_US
dc.descriptionPreviously density difference plots have given good qualitative results for many molecules. An example of this method, with plots for C2H n, n = 2,4,6 and C6H6, assesses the accuracy of a few DFT functionals. Generally all functionals are reasonably accurate but also show some large differences when compared to conventional ab initio densities. To improve upon these results the parameters of a new hybrid functional are optimised using a method inspired by the density difference plots. This functional exhibits some encouraging results but also shows many problems.en_US
dc.descriptionThe problems involved with the optimisation of the new functional lead to the development of the density difference index (DDI) to facilitate the comparison of two electron densities. Results indicate that the (DDI) yields a semi-quantitative measure of the distance between two electron densities. Also. the (DDI) values reveal a qualitative difference between DFT and conventional ab initio electron densities.en_US
dc.descriptionThe spin polarisation index (SPI) extends the results obtained by the (DDI) by quantitatively comparing the alpha and beta-electron densities in open-shell species. Generally the SPIs calculated with DFT are quite similar to conventional ab initio results. A few exceptions are found, though, where DFT substantially underestimates the SPI.en_US
dc.descriptionThe radial moments of the electron density are related to many different molecular properties and can be determined experimentally while also giving information on the spatial properties of different electron densities. Using a new analytical method for calculating these moments it is found that the DFT moments compare well with both experimental and QCISD results. The solvation effects for all methods are generally quite similar and there is evidence of rearrangement of the electron distributions upon dissolution.en_US
dc.descriptionThe results of the investigations of DFT electron densities indicate that improvements can be made. A reoptimisation of the parameters from Becke's three-parameter hybrid functional is carried out to improve the calculated electron density. The optimised parameters are found by fitting the DFT electron densities to MP2 and QCISD densities using the DDI. A selection of molecular properties, including the radial moments of the electron density and the SPIs of some open-shell species, calculated using the new functionals are compared to conventional ab initio results with only fair results. However, there are indications that the electron densities of the new functionals gave a reasonable approximation of the two reference electron densities.en_US
dc.descriptionThesis (Ph.D.)--Dalhousie University (Canada), 1999.en_US
dc.languageengen_US
dc.publisherDalhousie Universityen_US
dc.publisheren_US
dc.subjectChemistry, Physical.en_US
dc.titleNovel tools for studying electron densities: Investigation and design of exchange-correlation functionals for density functional theory.en_US
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dc.contributor.degreePh.D.en_US
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