Matches in SemOpenAlex for { <https://semopenalex.org/work/W90663484> ?p ?o ?g. }
Showing items 1 to 57 of
57
with 100 items per page.
- W90663484 abstract "Kohn-Sham density functional theory (DFT) is the most prevalent electronic structure method in chemistry. Whilst formally exact, in practice it affords reasonable accuracy with reasonable computational cost and is the method of choice when considering molecules of non-trivial size. The key quantity is the exchange-correlation energy functional, the exact form of which is unknown. Approximate exchange-correlation functionals, particularly B3LYP and PBE, are routinely applied to chemical problems. However, it is not possible to guarantee a given accuracy in advance, nor is there a systematic means of obtaining a more accurate answer. Existing functionals are applied to ever more challenging problems and the accuracy required of them is continually increasing the need for more accurate functionals is one of the major challenges in electronic structure theory. This thesis focuses on several approaches that attempt to address this issue. In chapter 1 the electronic structure problem is outlined and discussed in terms of the Schrodinger equation and solutions involving wavefunctions. In chapter 2, the formal foundations of DFT are presented and methods of approximating the exchange-correlation functional are introduced. A promising new direction for developing exchange-correlation functionals, through attenuation of the exchange term, is introduced and discussed in detail in chapter 3. The accuracy of such functionals is investigated and compared to that obtained from conventional approaches, with a particular emphasis on the dependence on the attenuation parameters. It is then demonstrated that attenuated functionals offer the prospect of significantly improved descriptions of excitation energies, particularly for those of charge-transfer character. Apphcation of attenuated functionals to excitation energies that are problematic for conventional functionals is undertaken in chapter 4. Insight into the conflicting performance of conventional methods for different charge-transfer excitations is provided through a consideration of the orbital overlap between the orbitals involved in an excitation. Through this overlap quantity, a diagnostic test is proposed that enables a user to judge in advance the reliability of excitation energies from conventional functionals. Attenuated functionals are then applied to other difficult properties in chapter 5. Firstly they are used to study the bond length alternation and band gap in poly acetylene and polyyne oligomers and infinite chains. Then they are used to calculate nuclear magnetic resonance parameters in both main-group and first-row transition metal systems, through the theoretically rigorous optimised effective potential method. An entirely different approach to functional development is considered in chapter 6, where the adiabatic connection formalism is introduced as an alternative method of obtaining the exchange-correlation functional. For a series of two-electron systems, exact input data is used to determine the applicability of a number of simple mathematical forms in modelling the exact adiabatic connection. The conclusions from these simple systems are then used to provide insight into the possibility of using this approach in functional development." @default.
- W90663484 created "2016-06-24" @default.
- W90663484 creator A5060170858 @default.
- W90663484 date "2009-01-01" @default.
- W90663484 modified "2023-10-18" @default.
- W90663484 title "Modern approaches to the exchange-correlation problem" @default.
- W90663484 hasPublicationYear "2009" @default.
- W90663484 type Work @default.
- W90663484 sameAs 90663484 @default.
- W90663484 citedByCount "0" @default.
- W90663484 crossrefType "dissertation" @default.
- W90663484 hasAuthorship W90663484A5060170858 @default.
- W90663484 hasConcept C113603373 @default.
- W90663484 hasConcept C121332964 @default.
- W90663484 hasConcept C121864883 @default.
- W90663484 hasConcept C152365726 @default.
- W90663484 hasConcept C28826006 @default.
- W90663484 hasConcept C33923547 @default.
- W90663484 hasConcept C41008148 @default.
- W90663484 hasConcept C62520636 @default.
- W90663484 hasConcept C86025842 @default.
- W90663484 hasConceptScore W90663484C113603373 @default.
- W90663484 hasConceptScore W90663484C121332964 @default.
- W90663484 hasConceptScore W90663484C121864883 @default.
- W90663484 hasConceptScore W90663484C152365726 @default.
- W90663484 hasConceptScore W90663484C28826006 @default.
- W90663484 hasConceptScore W90663484C33923547 @default.
- W90663484 hasConceptScore W90663484C41008148 @default.
- W90663484 hasConceptScore W90663484C62520636 @default.
- W90663484 hasConceptScore W90663484C86025842 @default.
- W90663484 hasLocation W906634841 @default.
- W90663484 hasOpenAccess W90663484 @default.
- W90663484 hasPrimaryLocation W906634841 @default.
- W90663484 hasRelatedWork W1555946707 @default.
- W90663484 hasRelatedWork W1966721657 @default.
- W90663484 hasRelatedWork W2073672585 @default.
- W90663484 hasRelatedWork W2090442705 @default.
- W90663484 hasRelatedWork W2142864517 @default.
- W90663484 hasRelatedWork W2312547514 @default.
- W90663484 hasRelatedWork W2463579414 @default.
- W90663484 hasRelatedWork W2519513486 @default.
- W90663484 hasRelatedWork W2737269131 @default.
- W90663484 hasRelatedWork W2968672900 @default.
- W90663484 hasRelatedWork W2970116811 @default.
- W90663484 hasRelatedWork W2995632896 @default.
- W90663484 hasRelatedWork W3092282471 @default.
- W90663484 hasRelatedWork W3127369373 @default.
- W90663484 hasRelatedWork W3129868659 @default.
- W90663484 hasRelatedWork W42723134 @default.
- W90663484 hasRelatedWork W615737156 @default.
- W90663484 hasRelatedWork W61961123 @default.
- W90663484 hasRelatedWork W810285161 @default.
- W90663484 hasRelatedWork W2944206741 @default.
- W90663484 isParatext "false" @default.
- W90663484 isRetracted "false" @default.
- W90663484 magId "90663484" @default.
- W90663484 workType "dissertation" @default.