# Suceptibility in QSGW+DMFT

The aim of this tutorial is to present how to get the magnetic and charge susceptibility using the impurity vertex. Until now, this part of the code is still in the develloping branch. To use it, it is strongly adviced to ask the devellopers first.

The Bethe Salpeter used in this tutorial and the Susceptibility calculated in this tutorial are explained in this pdf (LINK).

The differents step are :

1) For each inequivalent impurity, the impurity susceptibility has to be calculated. It is mandatory to calculated the impurty susceptibilities with the same number of fermionic Matsubara frequencies (call nomv) and bosonic Matsubara frequencies (nomb) for all susceptibility.

For each inequivalent impurity, transform the file tvertex.dat printed by the CTQMC solver using the function readvertex in the questaal package :

 readvertex tvertex.dat name_for_the_vertex.h5


the advantage of the h5 is that it is quicker to load it and, in general, ligher (tvertex.dat can be .

2) The bare susceptibility is calculated with lmfdmft. Fisrt, we need to specify the number of fermionic and bosonic matsubara frequencies : create a file with two interger as follow : ‘’’ 10 100 ‘’’ when 10 is the number of bosonic frequencies and 100 the number of fermionic frequencies then run lmfdmft as follow :

lmfdmft ybco -vnkabc=10 –gprt~mode=5~rsig=sig –chi0

It can be run with mpi.

it will compute chi0 on the k-mesh 10x10x10. Sometime, we do not need to comnpute chi0 on the full BZ but just on a subset of q point. It can be done by using the flags –qlist FORMAT OF qlist

it will produced a file call chi0.h5 which store the susceptibility. The structure of chi0.h5 (usefull for develloper) … … …

3) The Bethe Salpeter equation is done and print chi_s and chi_c in a h5 file using the python script : h5py has to be installed in your system MPI_OPT Sucept_multicix_mpi.py

chi_s and chi_c can be plot by reading this hdf5 file. This a example of python script to plot chis on the plan Q1,Q2