[QE-users] ESM model with vacuum/metal boundary condition (bc3)

[Minoru Otani]

Dear Prasenjit Ghosh,

Please refer to Figure 1 in the original ESM paper (PRB 73, 115407 (2006)). The position of the right edge of the unit cell is z_0​, while the position of the ESM region is z_1​. Thus, the definition of esm_w is as follows: esm_w​=z_1​−z_0​


Typically, we try to keep the unit cell size (z_0​) as small as possible. However, the position of the ESM region depends on the model you want to simulate. For example, if you are modeling a parallel plate capacitor with ESM, the position of z_1​ is determined by the thickness of the vacuum region between the electrodes. Please remember that z_1​ must be greater than or equal to z_0​, so esm_w​ is either positive or zero.

Best regards,
Minoru

> On Apr 23, 2024, at 19:16, Ghosh, Prasenjit <pghosh at iiserpune.ac.in> wrote:
> 
> Dear all,
> 
> I am trying to perform calculations for a charged system with assume_isolated = "esm" and using a vacuum/metal boundary condition (esm_bc='bc3').
> However, I am confused regarding how to choose the position offset for the start of the effective screening region (esm_w).
> Some preliminary calculations by varying esm_w suggests that the results (for eg. the electrostatic potential on the vacuum side, magnitude of the bias applied to the surface, etc.)
> strongly depends on the choice of the "esm_w" variable.
> 
> Can anyone please suggest how to choose an optimal value of "esm_w"?
> 
> Thanking you in advance.
> 
> With regards,
> 
> Prasenjit Ghosh
> IISER Pune
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