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["Chun Li " <chun.li@mf.mpg.de>]

Dear all,

 

Could anyone here give me some ideas? I am really confused about that. Thank you very much.

 

Best regards.

 

Chun Li

 

-----Original Message-----
From: Chun Li [mailto:chun.li@mf.mpg.de]
Sent: Thursday, November 18, 2004 6:52 PM
To: forum@abinit.org
Subject: RE: [abinit-forum] about berry phase

 

Dear Marek Veithen,

 

Thanks a lot for you kind help. I encountered one more question about

the polarization calculation using Berry phase method in abinit.

 

I wonder if the positive or negative of the obtained polarization

indicates the real polarization direction of the model. The reason why I

ask this is: according to the routine of berry phase, if the absolute

value of the obtained total phase is larger than 1, even a little

bigger, the code will give a positive value (suppose the value of the

total berry is negative), like below:

 

Summary of the results

 Electronic Berry phase    -8.483634287E-01

            Ionic phase    -1.531124789E-01

            Total phase    -1.001475908E+00

    Remapping in [-1,1]     9.985240924E-01

 

           Polarization     3.101809093E-02 (a.u. of charge)/bohr^2

           Polarization     1.774692648E+00 C/m^2

 

But it is very possible that the absolute value of the obtained total

phase is a little smaller than 1 (for example, change the dense of the

k-point). Then one will get the completely different result (I mean the

different directions), like below:

 

Summary of the results

 Electronic Berry phase    -8.350116714E-01

            Ionic phase    -1.531124789E-01

            Total phase    -9.881241503E-01

    Remapping in [-1,1]    -9.881241503E-01

 

           Polarization    -3.069502777E-02 (a.u. of charge)/bohr^2

           Polarization    -1.756208667E+00 C/m^2

 

I think the polarization of the same cell in the same direction should

be a certain value, at least its direction. So do you have some ideas

about this problem? Thank you.

 

Best regards.

 

Chun Li

 

-----Original Message-----

From: Marek Veithen [mailto:Marek.Veithen@ulg.ac.be]

Sent: Tuesday, November 09, 2004 2:58 PM

To: forum@abinit.org

Subject: Re: [abinit-forum] about berry phase

 

Dear Chun Li,

 

>1) What is the indeed difference between berryopt=1 and -1? Which is

>better?

> 

>

berryopt = 1 only works for kptopt = 2 or 3 while berryopt = -1 also

works

for kptopt = 1. The option berryopt = -1 is more efficient because it is

sufficient to sample the irreductible part of the Brillouin zone.

 

>2) Why I obtained much different polarizations for different berryopt?

>For example, the polarizations of zincblende structure are

>1.642499562E-01 C/m^2 and 8.674776685E-01 C/m^2 for berryopt=1 and -1

>respectively.

> 

>

In your input file, you use bdberry  1 24. That means, you compute

the Berry phase for 24 bands while the number of occupied bands

of ZnO is equal to 9. I modified your input file and I added a few

comments

(look for "MV"). You will see that berryopt = 1 and -1 provide exactly

the

same result.

 

Best regards,

Marek

 

--

Marek VEITHEN

Universite de Liege

Institut de Physique, Bat. B5

Allee du 6 aout, 17

B- 4000 Sart Tilman

BELGIUM

 

 

Phone : ++(32) (0)4-366.36.12

Fax   : ++(32) (0)4-366.29.90

E-mail: Marek.Veithen@ulg.ac.be