The ABINIT Users Mailing List ( CLOSED )

[fdv@u.washington.edu]

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.