# [Pw_forum] ESM method

Wed Jul 26 14:02:44 CEST 2017

```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 Angstrom? Please explain.

Thank you.

Rajesh

```