numeric value of electrostatic difference potential

[Sabyasachi Sen]

i) In electrostatic difference potential plot colored contour plot does not produce exact numeric value on a specific atom. Can you suggest any modification in python script which will give us the numeric value of the electrostatic potential difference between any two atom of choice.

ii) In a calculation with Au electrode-Central region-Au electrode run I noticed that Fermi energy of Au electrodes (both left and right) with LSDA functional and SZ basis is -0.74 eV while the same for the central region considering equivalent bulk as -4.0 eV. However, in transmission run Femi energy is shifted to zero as per the energy of the electrodes. Since, there is a huge difference in Fermi energy between the central region and the electrodes. Could you please clarify what is the importance of the Fermi energy of central region? or How does it influences the transport run.



 

[Anders Blom]

1. If you want the potential evaluated at two atomic positions, and know the difference between these two values, you could do

Code: python

pot = nlread("file.nc", ElectrostaticDifferencePotential)[0]
p1 = pot.evaluate(0.*Ang,0*Ang,0*Ang)
p2 = pot.evaluate(0.*Ang,0*Ang,1*Ang)
print p2-p1

where I assume you have evaluated the potential already and stored it in "file.nc", and the two atom positions are given as arguments to the evaluate method. You can - and should, probably - get the precise positions from the coordinate list rather than type them in. 2. The simple answer is that one should pay not attention to these numbers. They are absolute energies, with different zero points, and thus cannot be compared, not is it relevant except internally in the code in order to to align the Fermi levels of the different regions. Besides, there is no "central region Fermi level" - the whole point of the non-equilibrium calculation is that there is no Fermi distribution in the central region. The value you see in the "equivalent bulk" part is a pre-calculation to help convergence.