Seite - 11 - in Charge Transport in DNA - Insights from Simulations

CHAPTER2 TheoreticalBackground The aim of theoretical or computational chemistry is to describe molecules and their properties as accurately and efficiently as possible. Unfortunately,with cur- rentcomputationalpowernotbotharepossibleat thesametimefor largemolecules, e.g.biomolecules. Therefore, specialmethodsforsolvingmoreor lessspecific tasks were developed. The methods at hand for description of the dynamics of large biomolecules are themolecularmechanics (MM), shortly described in chapter 2.1, and the molecular dynamics (MD), described in chapter 2.2. As this work does notonly focuson themere structuresofbiomoleculesmore sophisticatedmethods have tobeused. Quantummechanicalmethods (QM)have tobeapplied (Chapter 2.3) for thedescriptionof charge transport andcharge transfer (CT) inmolecules. 2.1 MolecularMechanics Thedescriptionof all propertiesofmoleculeswithmethodsbasedon the relativis- tic time-dependent Schrödinger equation is very difficult, if not impossible, and very time consuming. Onehas to think aboutmethodswhichwill bemuch faster without losing toomuch of the desired accuracy. The properties of biomolecules 11