The ABINIT Users Mailing List ( CLOSED )

[verstraete@pcpm.ucl.ac.be]

Hello Fer,

Is your DW calculator GPL? Just asking...

I presume you've done the tutorials on Al and so on. There are additional 
parameters (occopt, tsmear) when you do a metal, and you need a lot more 
kpoints.

1) You definitely do not need to use a supercell. Running anaddb with a 
mesh of qpoints instead of just gamma (see tutorial 5) will allow you to 
interpolate the ifc and dynamical matrices for atoms far from the central 
one. You typically go to 20th neighbor, sometimes more.

2) You'll probably need a 10x10x10 kpoint grid (fcc shifted see 
tutorials), the cutoff should be 20-40 hartree. The rest you'll have to 
converge. I'd use GGA, but see "Narasimhan S, de Gironcoli S Ab initio 
calculation of the thermal properties of Cu: Performance of the LDA and 
GGA PHYSICAL REVIEW B 65 (6): Art. No. 064302 FEB 1 2002" for details.

3) wfoptalg is still quite experimental. Please try it and report any 
success/failure here.

Matthieu

On Wed, 20 Jul 2005, fdv@u.washington.edu wrote:

> Hello everybody,
>
>  Our group has developed a method to calculate Deby-Waller factors for 
> use in XANES and EXAFS simulations. The only input required are the 
> second derivatives of the energy. So far we have used force constants 
> from force fields, but we are interested in obtaining the derivatives ab 
> initio. We want to have a fast, quasi-black box method to obtain the 
> second derivatives for a varied number of solids, to within 10-15% 
> accuracy.
>
>  Following the tutorials and with a little experience from other plane 
> wave codes, I was able to set up an abinit calculation for Ge crystal 
> and obtained a dynamical matrix which results in very good DW factors 
> (compared to experiment). Now I'm trying to get values for Cu but I'm 
> running into some problems.
>
>  Here are some specific questions that I have:
>
> 1) I need to get the second derivatives of an atom and its first and 
> second neighbours at least. Is there any way to do this besides making a 
> large supercell? (I don't think there is, but I'm asking just in case.. 
> :-)
>
> 2) Does anybody have an input file for copper that is known to give 
> "reasonable" results (i.e. less than 10% error in the structural 
> constants, for example). I'm specially interested in the size of the 
> cell, the number of k-points, the energy cutoff, functional and 
> pseudopotential used and in the type and amount of smearing used. Most 
> of the plane-wave calculations that I've done in the past have dealt 
> with insulators. I need an initial push with metals. (Feel free to 
> suggest any kind of reading that you might think would be of interest).
>
> 3) I have a cluster and have a parallel version of the code compiled. It 
> scales quite well when the nuber of k-points is large and the size of 
> the cell is small. When I try a large supercell and a reduced number of 
> points, some of the processors are not used. I am runnin the 4.5.3 
> version and when I tried the wfoptalg=4 option but the code complained 
> that only 0-3 are allowed. How do I increase the performace for a large 
> cell with fewer k-points?
>
> Well, I think that's all for now and sorry for the long post.
>
> Best regards, Fer.

--
================================================================
Matthieu Verstraete             mailto:verstraete@pcpm.ucl.ac.be
PCPM, Boltzmann, pl. Croix du Sud, 1        tel: +32 10 47 33 59
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