Details

Autor(en) / Beteiligte

• Hindle, Sally Ann

Titel

A new quantum mechanical/molecular mechanical method for modelling biological and solid state systems

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2000

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Quantum Mechanical / Molecular Mechanical modelling techniques have been widely used for some time for investigating the reactions of large systems such as enzymes. The reacting centre of the system forms a region included in a higher level calculation, while the bulk of the system is treated at a lower level. Often, these techniques employ a method of saturating dangling bonds which are formed at the interface between the two regions, with hydrogen atoms. This method may not always be satisfactory and recently alternatives have appeared in the literature that eliminate the need for these terminating hydrogens. These methods use localised orbitals or sets of atomic orbitals in place of the dangling bonds, to form terminations. One such method is the Local Self Consistent Field method (LSCF). This thesis describes a new implementation of LSCF into a well-known molecular modelling package and the subsequent modification, refinement and evaluation of the LSCF method. This evaluation is extended to the application of LSCF in modelling of enzymatic and periodic systems. A Quantum Mechanical / Molecular Mechanical method that terminates dangling bonds with hydrogens was used as a benchmark against which LSCF could be compared. The evaluation showed LSCF to be a viable Quantum Mechanical / Molecular Mechanical modelling method. When LSCF was applied to more specific biological modelling problems its performance was good; comparable to that of the hydrogen terminating method. However, in solid state cases LSCF suffered greatly from convergence problems and where successful, convergence was achieved in long periods of time compared to the hydrogen terminating method.