# [Pw_forum] ESM method

Rajesh creativeidleminds at gmail.com
Wed Jul 26 14:14:15 CEST 2017

```Dear Minoru,
Thanks for quick response. Here AA=angstrom?? I tried esm method in
vc-relax calculations with two boundary conditions
1. pbc and 2. bc1.

For pbc conditions the energy comes out too be negative but for bc1 it was
positive ( with no esm_w value). Energy of solids is always negative. So
where I am wrong?

Thanks.

Rajesh

On Wed, Jul 26, 2017 at 5:32 PM, 大谷実 <minoru.otani at aist.go.jp> wrote:

> Dear Rajesh,
>
> I can not fully understand your configuration. But let me suppose you have
> a single graphene
> sheet in a calculation cell with 15AA vacuum on both sides.
>
> L_z = 15AA + graphene sheet (0 AA) + 15AA = 30 AA
> The graphene sheet is located at z=0.
>
> For bc1 calculation, you do not need to use esm_w. For bc2 or bc3, if you
> want to put ESM(metal) electrode at the position of z= +/- 15AA (for bc2)
> or z= +15AA (for bc3), esm_w = 0.0. The esm_w specifies the offset value of
> the ESM(metal) electrode position from the cell edge (z=+/- L_z/2). Thus,
> if you want to put the electrode on z= + 18AA, the esm_w must be 3AA.
>
> Best regards,
> Minoru
> ________________________________________
> From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf
> of Rajesh <creativeidleminds at gmail.com>
> Sent: Wednesday, July 26, 2017 8:34:20 PM
> To: PWSCF Forum
> Subject: [Pw_forum] ESM method
>
> Dear Users,
>
> in the manual I find this "ESM region begins at z = +/- [L_z/2 + esm_w]".
> Suppose I have graphene sheet of with 3.33Angstrom as its thickness and I
> want to apply a 15Angstrom vacuum on both sides of the sheet. What are z
> and L_z/2 here?? is L_z/2=3.33A?? and Then what will be the value of
> position offset esm_w?? is esm_w=15angstrom?? and z=3.33+15+15=33.3
>
>
> Thank you.
>
>
>
> Rajesh
>
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