Simulating Chiral Induced Spin Selectivity using Non-Equilibrium Green's Functions

Simulating Chiral Induced Spin Selectivity using Non-Equilibrium Green's Functions

Vroomans, Tim (TU Delft Applied Sciences)

Thijssen, Jos (mentor)

Delft University of Technology

2019-01-30

In this thesis a method is proposed to improve upon the Non-Self-Consistent Green's function transport calculation used by the Amsterdam Density Functional package (ADF) made by Software for Chemistry and Materials (SCM) so ADF is able to simulate Chiral Induced Spin Selectivity (CISS). CISS is an effect that causes spin polarisation to occur in currents that flow through chiral molecules, such as DNA. In this thesis, Helicene is chosen since it has a helical structure but it is also a relatively simple molecule to simulate. In the calculations the helicene is attached to two gold contacts via a sulfur atom on each side. Gold is chosen for its strong spin-orbit coupling, which is thought to cause the effect. The native Green's function transport calculation uncouples the spin-orbitals into their two spin directions, it essentially preforms the same calculation twice for both spin direction. Because the spin directions are treated separately this method neglects any interactions between electrons of different spin. Therefore no spin polarisation will arise in the absence of a magnetic field. The proposed method improves on this by accounting for the full spin-orbitals, and therefore their potential overlap with each other. Because the potential interactions between orbitals occupied by electrons of different spin, spin-flip interactions are taken into account in the Green's function when calculating the transmission of the Helicene. This then gives rise to potential spin polarisation in the current. Due to a lack of time and an overabundance of run-time errors in the FORTRAN code used to implement the proposed method in ADF 2019, no results could be obtained to confirm or deny this.

http://resolver.tudelft.nl/uuid:961b8e1c-fd80-43aa-a17b-925e173ec6c7

Student theses

bachelor thesis

© 2019 Tim Vroomans