Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids
Most force field models for Room temperature ionic liquids cannot properly elucidate statics and dynamics. It is in this context that we set to assess the most efficient way to model RTILs while maintaining the integrity of the liquids statics and dynamics. The development approach begins with the i...
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | Eng |
| Published: |
Department of Chemistry
2016
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613286379290624 |
|---|---|
| access_status_str | Open Access |
| author | Mngadi, Vela |
| author2 | Venter, Gerhard A |
| author_browse | Mngadi, Vela Venter, Gerhard A |
| author_facet | Venter, Gerhard A Mngadi, Vela |
| author_sort | Mngadi, Vela |
| collection | Thesis |
| description | Most force field models for Room temperature ionic liquids cannot properly elucidate statics and dynamics. It is in this context that we set to assess the most efficient way to model RTILs while maintaining the integrity of the liquids statics and dynamics. The development approach begins with the investigation of the effects that the linear scaling of partial atomic charges on nonpolarisable force fields from a reference potential has on the structure and dynamics of the room temperature ionic liquids (RTILs) 1-butyl-3-methylimidazolium tetraflouroborate [C4MIM][BF4] and 1-butyl-3-methylimidazolium hexaflourophosphate [C4MIM][PF6]. The results show that the three-dimensional structure of the liquid is changed ever so slighter by the linear scaling of atomic charges. While dynamic properties such as viscosity and self-diffusion coefficients were majorly affected by charge scaling. Self-diffusion coefficients that span a range of four orders of magnitude between the original model and the scaled model where the ionic charge was ±0.6 e. Viscosity estimates calculated using the Green-Kubo and the Einstein relationships revealed that the linear scaling of atomic charges results in increased mobility of the simulated liquid. Implicit inclusion of polarisation effects was investigated, Here a new charge scheme development using Quantum mechanics/Molecular mechanics (QM/MM) methods in CHARMM 35 interfaced with GAMESS-UK was propose. The atomic charges were derived from liquid phase calculations using an iterative procedure. This was carried out for individual ions and cation-anion pairs, for the analysis of charge transfer, within the liquid environment. The results obtained gave predictions of density, liquid structure and self-diffusion coefficients that were in excellent agreement with experimental data available. This method is preferable over the commonly used charge scaling methodology which is deem as an unphysical approach for the simulation of [C4MIM][BF4] and [C4MIM][PF6]. A polarisable force field based on the Drude oscillator model is presented. The model proves to be most effective for the simulation of RTILs. The force field accurately reproduced experimental results for the physicochemical properties reviewed. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/20001 |
| institution | University of Cape Town (South Africa) |
| language | Eng |
| last_indexed | 2026-06-10T12:33:43.673Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Department of Chemistry |
| publisherStr | Department of Chemistry |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/20001 Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids Mngadi, Vela Venter, Gerhard A Chemistry Most force field models for Room temperature ionic liquids cannot properly elucidate statics and dynamics. It is in this context that we set to assess the most efficient way to model RTILs while maintaining the integrity of the liquids statics and dynamics. The development approach begins with the investigation of the effects that the linear scaling of partial atomic charges on nonpolarisable force fields from a reference potential has on the structure and dynamics of the room temperature ionic liquids (RTILs) 1-butyl-3-methylimidazolium tetraflouroborate [C4MIM][BF4] and 1-butyl-3-methylimidazolium hexaflourophosphate [C4MIM][PF6]. The results show that the three-dimensional structure of the liquid is changed ever so slighter by the linear scaling of atomic charges. While dynamic properties such as viscosity and self-diffusion coefficients were majorly affected by charge scaling. Self-diffusion coefficients that span a range of four orders of magnitude between the original model and the scaled model where the ionic charge was ±0.6 e. Viscosity estimates calculated using the Green-Kubo and the Einstein relationships revealed that the linear scaling of atomic charges results in increased mobility of the simulated liquid. Implicit inclusion of polarisation effects was investigated, Here a new charge scheme development using Quantum mechanics/Molecular mechanics (QM/MM) methods in CHARMM 35 interfaced with GAMESS-UK was propose. The atomic charges were derived from liquid phase calculations using an iterative procedure. This was carried out for individual ions and cation-anion pairs, for the analysis of charge transfer, within the liquid environment. The results obtained gave predictions of density, liquid structure and self-diffusion coefficients that were in excellent agreement with experimental data available. This method is preferable over the commonly used charge scaling methodology which is deem as an unphysical approach for the simulation of [C4MIM][BF4] and [C4MIM][PF6]. A polarisable force field based on the Drude oscillator model is presented. The model proves to be most effective for the simulation of RTILs. The force field accurately reproduced experimental results for the physicochemical properties reviewed. 2016-06-10T07:39:29Z 2016-06-10T07:39:29Z 2015 Master Thesis Masters MSc http://hdl.handle.net/11427/20001 Eng application/pdf Department of Chemistry Faculty of Science University of Cape Town |
| spellingShingle | Chemistry Mngadi, Vela Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids |
| thesis_degree_str | Master's |
| title | Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids |
| title_full | Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids |
| title_fullStr | Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids |
| title_full_unstemmed | Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids |
| title_short | Development of a force field with condensed phase consistent charges for N,N' - dialkylimidazolium room temperature ionic liquids |
| title_sort | development of a force field with condensed phase consistent charges for n n dialkylimidazolium room temperature ionic liquids |
| topic | Chemistry |
| url | http://hdl.handle.net/11427/20001 |
| work_keys_str_mv | AT mngadivela developmentofaforcefieldwithcondensedphaseconsistentchargesfornndialkylimidazoliumroomtemperatureionicliquids |