The ABINIT Users Mailing List ( CLOSED )

["D. R. Hamann" <drh@bell-labs.com>]

Dear Chun,

I believe that you need to study the literature of the modern theory
of polarization to be able to answer these questions.  These are not
Abinit issues.  Perhaps chapter 22 of Richard Martin's new book (see
http://www.abinit.org/ABINIT/Infos_v4.4/bibliography.html) would be a good
starting point.

D. R. Hamann

Chun Li wrote:

Dear Hamann,

Thank you for your kind help.

Frankly, I am not so familiar with the theory of Berry phase. I just
find from some materials that indicating the spontaneous polarization of
ZnO can be viewed as the difference between that of the wurtzite (polar)
and zincblende (nonpolar) structures. I wonder if the Berry phase method
in ABINIT calculates the spontaneous polarization automatically, or
should I calculate the polarizations of wurtzite and zincblende
structures respectively?

By the way, if I want to calculate the polarizations of slab model of
ZnO, I think the results will still depend on the thickness of the
vacuum region (similar with the case in linear-response calculation).
How to solve this kind of problems? Are there still debates on that? I
think there should be some experienced users who can give me some advice
or suggestions. Thank you in advance.

Best regards.

Chun Li

-----Original Message-----
From: D. R. Hamann [mailto:drh@bell-labs.com] 
Sent: Wednesday, November 03, 2004 10:44 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] RE: about DDB file

Dear Chun,

A preprint on the formalism for the elastic and piezoelectric tensors
as implemented in Abinit is available:
http://arxiv.org/abs/cond-mat/0409269

The polarization is a vector, not a tensor, and can be calculated in an
Abinit ground-state
calculation by setting berryopt and related variables.

D. R. Hamann

Chun Li wrote:

Dear Hamann,

You are right. The piezoelectric constants of the supercell are
different for different width of the vacuum layer. Is there any material
that introduces the specific arithmetic of this kind of calculations in
abinit? 
One more question, I wonder if the polarization tensor can be obtained
by abinit rf calculation followed with anaddb.

Thank you and best regards.

Chun Li

-----Original Message-----
From: D. R. Hamann [mailto:drh@bell-labs.com] 
Sent: Friday, October 29, 2004 4:55 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] RE: about DDB file

Dear Chun,

Abinit can do the calculation.  The results, since they are
non-physical,
will depend on the width of the vacuum region.  No experiment can
measure 
the effect of a surface on the elastic tensor of a material.  While
there
was debate in the literature about the role of surface charge in
piezoelectricity, it was firmly established to be a bulk property by 
Richard Martin about 20 years ago.

D. R. Hamann


Chun Li wrote:

Dear Hamann,

Thank you for your reply.

The problem has been resolved by using mrgddb to merge the DDB files
into a complete one.

About the serious issue you mentioned, I wonder if it is only for bulk
model that the elastic tensor and piezoelectric tensor can be calculated
meaningfully in ABINIT. If it is true, how to calculate the
piezoelectricity of film or surface structure models using abinit? My
intent is just to perform such simulations. Could you give me some
ideas? Thanks a lot.

Best regards.

Chun Li







  

-- 
D. R. Hamann				Phone: 908-582-4454
Director, Theoretical Materials    	Fax:   908-582-4702
  Physics Research (retired)		email: drh@physics.bell-labs.com
Bell Laboratories 
Lucent Technologies
700 Mountain Ave, Room 1D-371
Murray Hill, NJ 07974-0636 USA