[QE-users] Finite electric field polarisation

[Terry Frankcombe]

Hi Mostaffa

To close the loop here, I appreciate your response, though I am familiar with the Modern Theory and agree that the dipole from any particular cell is not useful in isolation.  However, the calculated dipole numbers should not jump from e.g. -10 to +5 in the last iteration as the SCF converges!

Nonetheless, it turns out the problem is something wrong with the centrally-provided build on the machine I'm using.  When I compile pw.x myself (ver. 6.7, but meh) on the same or another machine, the dipoles converge as I expect them to.

Thanks for your help.

Ciao
Terry


________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Mostafa Youssef via users <users at lists.quantum-espresso.org>
Sent: Tuesday, 19 January 2021 7:44 PM
To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Finite electric field polarisation

Dear Terry,

The dipole results need post-processing. One needs to subtract n x polarization quantum to obtain a meaningful polarization.  n is an integer.

Consider a simple dielectric like MgO at zero field. pw.x may give you different dipoles in all directions, although physically in all directions the net dipoles are zero. If you post-process as I indicated above you get zero dipole as it should.

A good starter on this topic is this paper:
https://www.sciencedirect.com/science/article/abs/pii/S0022459612003234
A free arXiv version of it is also available.



Mostafa
AUC

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