# questions related with DIIS

*From*: Hong <hong $#at#$ chem.duke.edu>
*Organization*: Duke Unversity
*Subject*: questions related with DIIS
*Date*: Wed, 19 Dec 2001 18:28:19 -0500

Dear CCLers,
I am using Pulay's DIIS method to accelerate the SCF convergence in my
Kohn-Sham codes, and I have several questions concerned with its
implementations. How many previous vectors ( density in my case) should be used
to get optimal efficiency? Is the DIIS equations always solvable, which I
means, is it possible that the set of linear equations become
linear-dependent? I also found in some cases some coefficients are negative
especially when the number of vectors is small. Is that reasonable? I found
if I use the output density as the next input density directly whenever there
are negative coefficients, the total performance is better. I guess such
problems have been investigated by some researchers, but I don't know where to
find the relevant papers. The only paper about DIIS I have at hand is Pulay's
(1982 CPL). Would you give me some advices?
I appreciate your help!
Hong