Gate and Bias potentials¶
In this tutorial we will show how to include a Gate and Bias potentials in NEGF calculations.
Download the lead and molecules .xyz files:
The system studied in this tutorial is just a toy system.
Set up the system:
- 1. Select the file Li_lead.xyz as Lead2. Fill the central region with 4 layers of lead material3. Set the tips as shown in the figure. (Select left two atoms and click the + after Left tip, similarly for the right tip.)4. Set the right and left lead offsets to -8.5 and 8.5 respectively5. Select Method → self-consistentImport the file CuAg.xyz by clicking on File → Import Coordinates…
To apply a gate potential of 0.1 Volts for the CuAg molecule:
- 1. Select the CuAg molecule2. Click on the + next to Potential region3. Set the gate potential to 0.1 V
You can check the regions in the Model → Regions panel. You will see there the right_tip, left_tip and gate_potential regions. Use the checkboxes to see them individually.
We will now apply a bias potential of 0.1 Volt, with a ramp-potential from -3.0 to 3.0 Angstrom (see picture below), do not forget to change the unit to Angstrom, the choices shown by clicking on the unit:
You can only apply a bias potential for the self-consistent and self-consistent + align NEGF methods
- 1. Set the bias potential Voltage to 0.12. Set the bias potential range to -3.0 and 3.0 respectively
we are now ready to run the calculation:
- Click on File → SaveRun the calculation with File → RunWait for the calculation to finish
The current (in atomic units) is saved on the binary .rkf file.
- Click on SCM → KFBrowserActivate Expert mode by clicking on File → Expert modeClick on File → Related Files → band.rkfLook for the NEGF sectionClick on the small arrow next to the NEGF sectionThe current should be “-0.00289”
You can also extract this information using amsreport:
amsreport band.rkf "NEGF%current"
The Current vs Bias plot you can visualize with AMSspectra is computed from a the transmission function at fixed bias, and it is therefore just an approximation of the real Current vs Bias characteristic. If you want to compute the actual Current vs Bias characteristic you have to run multiple calculations using different bias potentials.