For some understanding about the gate voltage

[xhsh]

Hello, Dear All,

I am thinking about the gate voltage. Now we can add a metallic region or a dielectric region to the the central region. I want to know, what is the difference between this new method and the old method of shifting the onsite energy (like in version 08.10)? By the way, in the old method, do we just change the diangonal terms H_ii, but not the off-diagonal terms H_ij?

Thanks.

[Anders Blom]

There are several important differences. Indeed the old method only shifted H_ii, and all (selected) atoms were shifted by the same, fixed amount. In the new approach the electrostatic gates are included in the self-consistent procedure, so atoms will have different shifts depending on the positions and also the response of the electron cloud to the field is taken into account.

[xhsh]

There are several important differences. Indeed the old method only shifted H_ii, and all (selected) atoms were shifted by the same, fixed amount. In the new approach the electrostatic gates are included in the self-consistent procedure, so atoms will have different shifts depending on the positions and also the response of the electron cloud to the field is taken into account.

Many thanks for your reply, Anders. But how is the new gate voltage included in the self-consistent procedure? Do we solve the Poisson equation in another way, namely, by the multigrid method in the real space, and the gate voltages are taken as the boundary values of the Hartree potential? If this is the case, then we will have different dielectric constants in different parts of the central region and we may not use the FFT solver any more, right?

[Anders Blom]

Correct on both accounts

[xhsh]

Then I have other two questions:

1. Can we add a dielectric region to the left and right electrodes? I mean that, can we add a continuum dielectric region to the whole system, including the electrodes and central region?

2. Shall we always add a metallic region on the top or bottom of a dielectric region? I am wondering about this since I see it from one example in the manual. Is the value of the hartree potential in the metallic region set to a constant, namely, the gate voltage, when solving the Poisson equation?

Many thanks again.

[Anders Blom]

1. Yes, that's posible.
2. Anything you place outside a metallic region will not really be included in the calculation since the metal (which indeed has a constant Hartree potential) screens all electric fields.