Simulating the Charge Transfer Process Along Molecular Wires

Molecular wires promise the ultimate miniaturisation of electronics by transporting electrons long distances along polymeric chains. The mechanism for this charge transfer (CT) seems to be a hopping-type behaviour, with the electrons moving between the monomer sites. One of the best molecular wires is DNA along which CT can occur for many nanometres, with a sequence dependent behaviour [1]. It is widely accepted that the CT along a polymer takes place via a site-hopping mechanism and simulations have been performed using models to investigate, for example the dependence of the transfer rate on the electronic structure of the system [2]. These
simulations, however, rarely include the quantum mechanical nature of the nuclei. This must be done when the coupling between electrons and nuclei dominate the dynamics, in what are termed non-adiabatic effects, leading to behaviour that cannot be modeled by classical mechanics. Such coupling is known to be important in a range of systems in which CT takes place, particularly after photo-excitation.
The aim of this project is to use quantum dynamics simulations to study the mechanism of the CT in polymers and related systems, solving the time dependent Schrodinger equation (TDSE) as accurately as possible to include all quantum effects [3]. Of particular interest will be the importance of the coupling between the vibrational and electronic motion. Various models and methods will be examined, including using state-of-the-art direct dynamics simulations that calculate the potential energy surfaces on-the-fly as they are required [3]. This solves the TDSE using atomistic information and gives a complete chemical picture of the physical process. Molecular wires promise the ultimate miniaturisation of electronics by transporting electrons long distances along polymeric chains. The mechanism for
this charge transfer (CT) seems to be a hopping-type behaviour, with the electrons moving between the monomer sites. One of the best molecular wires is DNA along which CT can occur for many nanometres, with a sequence dependent behaviour [1]. It is widely accepted that the CT along a polymer takes place via a site-hopping mechanism and simulations have been performed using models to investigate, for example the dependence of the transfer rate on the electronic structure of the system [2]. These simulations, however, rarely include the quantum mechanical nature of the nuclei. This must be done when the coupling between electrons and nuclei
dominate the dynamics, in what are termed non-adiabatic effects, leading to behaviour that cannot be modeled by classical mechanics. Such coupling is known to be important in a range of systems in which CT takes place, particularly after photo-excitation. The aim of this project is to use quantum dynamics simulations to study
the mechanism of the CT in polymers and related systems, solving the time dependent Schrodinger equation (TDSE) as accurately as possible to include
all quantum effects [3]. Of particular interest will be the importance of the coupling between the vibrational and electronic motion. Various models and
methods will be examined, including using state-of-the-art direct dynamics simulations that calculate the potential energy surfaces on-the-fly as they
are required [3]. This solves the TDSE using atomistic information and gives a complete chemical picture of the physical process. 1. Wohlgamuth et al Anal. Chem. (2013) 85: 8634 2. Lambroupoulos et al Phys. Rev. E (2016) 94: 062403 3. Beck et al Phys. Rep. (2000) 324: 1 4. Richings et al Int. Rev. Phys. Chem. (2015) 34: 269