The ABINIT Users Mailing List ( CLOSED )

["Andrew M. Rappe" <rappe@sas.upenn.edu>]

Dear Fernando,

What category of material or system are you studying?  

LDA is renowned for giving pretty accurate interatomic force constants
even though it is not an exceedingly accurate functional.  There are
many things that must be correct for you to get accurate interatomic
force constants.  It doesn't strike me as likely that the functional
is your dominant error (although I suppose it's possible).

Can you be specific about what systems you are studying, and what your
computational approach is?  Perhaps we can suggest other sources of
error.

Sincerely,
Andrew M. Rappe

On Tue, Aug 22, 2006 at 08:39:02AM +0200 or thereabouts, Anglade 
Pierre-Matthieu wrote:
> Hi,
> 
> Have you tryed a look at the different functionnals readily available
> in abinit ? For instance I have heard that using "ixc=9" may give some
> much more accurate results.
> 
> regards
> 
> PMA
> 
> On 8/21/06, fer@tiziano.phys.washington.edu
> <fer@tiziano.phys.washington.edu> wrote:
> >Hi..
> >
> >  As I have probably mentioned here before, we have been working on 
> >  calculating EXAFS Debye-Waller factors using the dynamical matrices 
> >  generated by abinit. The whole approach works quite well, but we are not 
> >  totally satisfied by the results we get from either LDA (PW92) or GGA 
> >  (PBE). For us it is quite crucial getting the interatomic force constant 
> >  accurately. We have found that they depend a lot on the crystal lattice 
> >  that we use, and therefore we need to be able to find a way to realiably 
> >  predict both the crystal lattice and the force constants simultaneously. 
> >  Its seems that neither PW92 nor PBE can do this.
> >
> >We got in contact with John Perdew and he suggested we try the meta-GGA 
> >TPSS and we have tried to do so with the implementation already available 
> >in Gaussian 03. for reasons I don't what to discuss here, this 
> >implementation has several drawbacks when it comes to solid states.
> >
> >Therefore, I was wondering if anyone has implemented TPSS into abinit 
> >already. I did a search on the source and found that nanoquantaxc has 
> >TPSS, but I really don't know how to integrate it into my binaries nor how 
> >to call it. Any experience, instructions, etc, etc, in this regards would 
> >be greatly welcome.
> >
> >Best regards and thanks in advance, Fer.
> >
> >Ubi dubium ibi libertas.
> >*******************************************************************************
> >Fernando D. Vila                Voice    (206)543-9697
> >Department of Physics           Fax      (206)685-0635
> >University of Washington        E-mail   fdv@u.washington.edu
> >Seattle, WA 98195, USA          WWW      http://faculty.washington.edu/fdv
> >*******************************************************************************
> >
> 
> 
> -- 
> Pierre-Matthieu Anglade