How do I set up the geometry for transport calculations?
To calculate the electronic structure of a system under external bias, TranSIESTA attaches the system to semi-infinite electrodes which extend to the left and right of the contact region
The system is a combination of two parts,
- The Left and the Right bulk electrodes (Bulk): defined by two periodic parts
- The Scattering Region (SR): A finite part. It provides the functionality of the device, and causes the electrons and holes traveling between the two electrodes to be scattered. Contains the ‘contact’ (C) region and part of the right (R) and left (L) electrodes
Below are two general tips to follow when setting up the electrodes
- The contact region (C) should be large enough so that Left and Right electrodes do not interact with each other.
- Left and Right Leads regions should be smaller or equal to the cells used in the bulk calculation of the electrodes
The following figure shows examples of incorrect system configurations: a) Too short electrode, too short device, b) too short device, c) too short electrode.