2012/12/17 Emanuel Gull <emanuel.gull@gmail.com>

Hi Steffen:

>
> right now I'm working on a LDA+DMFT code and want to use the Hybridization
> Impurity Solver from the ALPS package.

great! Welcome!

> I have two questions regarding the implementation of the Impurity solver
> and would be very glad if you could provide me with some guidiance:
>
> My first question is, what is the best way to implement the impurity
> solver in a C++ code?
> What I've done so far is the following:
> I'm using the newest ALPS code version 2.1.1-r6176.

The current ALPS version is alps-2.1.1-r6560-src, available as the 'nightly' build on the homepage and via anonymous svn. If you're thinking of developing a code I would strongly recommend working with the svn version.

The old hybridization code with which you were working has been completely rewritten; that rewrite is now part of ALPS instead of the old code. You can find a documentation of it in doc/hybdoc.pdf.

> Another problem that I have, but want to adress after I resolved my first
> question, is that the GF from the Impurity Solver is not decaying like
> 1/w_n but with some factor ~ 1/1.5w_n. I'm using the Legendre
> representation of the GF and transform it back for further use in the DMFT
> cycle.
> Do you know a possible reason for this? Is this simply caused by too few
> Sweeps or Legendre coefficients?

Probably not enough Legendre coefficients or too much noise on the coefficients. The error propagation with Legendre coefficients is a bit tricky: the Fourier transform means that Matsubara coefficients are highly correlated. To make sure: simulate twice as long and see if anything changes.

Cheers,
Emanuel