The ABINIT Users Mailing List ( CLOSED )

[Philippe Ghosez <Philippe.Ghosez@ulg.ac.be>]

Dear Nicola,

the computation of Z* in zero field for ALL the atoms in the unit cell 
was already
previously accessible by linear response from the ddk and electric field
perturbation ONLY : i.e. calculation of the optical dielectric constant 
is also  providing
the Z* on all the atoms in the same run using a non-stationary 
expression with no
need to displace all the  uniquivalent atoms independently). Except if 
I missed something
I do not think the new implementation helps here.

Now I agree that the calculation of Z* in finite field provides an 
interesting alternative
way (to computation of  third-derivatives by linear response) for the 
Raman
efficiencies since the dchi/dtau can be alternatively written dZ*/dE 
and are now
easily accessible by finite diffirence as shown in the paper of Xinjie.

By the way, was this new feature implemented also for spin-polarized 
systems?

Best wishes,

Philippe.


On 05 Sep 2007, at 05:57, Nicola Marzari wrote:

> One side comment - it can become more efficient if the unit cell 
> contains many inequivalent atoms.
>
> Suppose you have 100 atoms - usually, you would need to displace each 
> of them, one by one, in the three crystallographic directions, and
> calculate the resulting polarization (this can be done either with
> linear-response theory, i.e. as the response to an infinitesimal 
> displacement, or with the Berry phase, as the response to a finite 
> one).
>
> Instead, you can apply a small electric field three times (in 3 non 
> equivalent directions), and you have right away the effective charges 
> for all the 100 atoms. Similar considerations apply, say, if you 
> wanted
> to calculate Raman couplings.
>
>
>                                 nicola
>
>
> Xinjie Wang wrote:
> > Hi David,
> > This feature (B.10) does not give more efficient/accurate calculations
> > of the static dielectric properties. It allows the calculation of
> > electric-field-dependence of Born effective charges and dielectric 
> > tensor. You can read this paper, Phys. Rev. B 75, 115116 (2007),
> > for details.
> > Regards,
> > Xinjie
> > david.hendry@mandmd.com.au wrote:
> > > Dear Abinitors,
> > >
> > > I'm interested in the static dielectric constant of 
> > > ceramics/insulators.  I notice the latest release notes of Abinit: 
> > > "B.10 Born effective charges and dielectric tensor calculations can 
> > > now be computed in a finite electric field." Does this feature or 
> > > any other new feature (from 5.3.4) allow a more efficient/accurate 
> > > calculation of the static dielectric properties?
> > >
> > > Sincerely,
> > >
> > > David.
>
>
> --
> ---------------------------------------------------------------------
> Prof Nicola Marzari   Department of Materials Science and Engineering
> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
> tel 617.4522758 fax 2586534 marzari@mit.edu http://quasiamore.mit.edu
--------------------------------------------------
Philippe GHOSEZ
Universite de Liege
Institut de Physique, Bat. B5
Allee du 6 aout, 17
B- 4000 Sart Tilman
BELGIUM

Phone : ++(32) (0)4-366.36.11
Fax   : ++(32) (0)4-366.36.29
E-mail: Philippe.Ghosez@ulg.ac.be

http://www.ulg.ac.be/phythema
--------------------------------------------------