[Wien] Interplane distance optimization for graphite

[Tran, Fabien]

Hi,


The gradient between the planes becomes larger and larger when the C axis increases, see lower panel of Fig. 13 in

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.80.195109

This favors larger equilibrium C when a GGA is used (larger gradient means more negative xc-energy) compared to using LDA.

This is just by luck that LDA is not bad for graphite.


F. Tran


________________________________
From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of delamora <delamora at unam.mx>
Sent: Tuesday, November 12, 2019 5:28 PM
To: wien at zeus.theochem.tuwien.ac.at
Subject: [Wien] Interplane distance optimization for graphite

Dear WIEN community,
I have a technical question;
I try to optimize the graphite unit cell and when I try to get the interplane axis, C axis, I get a different answer if I use GGA or LDA; with GGA I get a large value, but with LDA I get the correct answer.
My intuition says that between planes the electron charge density is so low that the gradient of the GGA is irrelevant, but the approximations made for GGA break down in this situation.

Saludos

Pablo
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