# [Pw_forum] ESM method

Wed Jul 26 14:48:57 CEST 2017

```Dear Rajesh,

Yes, AA is angstrom. Currently you can not use vc-relax. You can do a geometry optimization with fixed cell so you can use “relax". Regarding the positive total energy, first, you should try the ESM_example calculations and compare the results with the reference results. Did you get reasonable results? If yes, I can not understand the origin of your problem now.

Best regards,
Minoru
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Minoru Otani
National Institute of Advanced Industrial Science and Technology
Research Centre for Computational Design of Advanced Functional Materials
email : minoru.otani at aist.go.jp<mailto:minoru.otani at aist.go.jp>
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On Jul 26, 2017, at 21:14, Rajesh <creativeidleminds at gmail.com> wrote:

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<mailto: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<mailto:pw_forum-bounces at pwscf.org> <pw_forum-bounces at pwscf.org<mailto:pw_forum-bounces at pwscf.org>> on behalf of Rajesh <creativeidleminds at gmail.com<mailto: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 Angstrom? Please explain.

Thank you.

Rajesh

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