steps to calculating spin fluctuation sigma:
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DFT calculation:
- get real space density from espresso: iotk convert *.dat *.xml

i) calculate non-interacting susceptibility: use skip_epsilon
ii) calculate inverse epsilon: skip_chi
iii) convert non-interacting susceptibility to ascii: use jl_readchi.cplx.x
=> input file is jl_readchi.inp: contains file name (chimat or chi0mat)
iv) run getqffchi.m to obtain spin susceptibility
=> need charge density (cd.dat), nmtx.dat, fulleps.dat, gvecs.dat
=> V_spin in Wdat
v) convert spin susceptibility to binary using jl_rweps.cplx.x
=> input file is jl_rweps.inp: needs name of epsmat file from step ii) (epsmat or eps0mat)
vi) run BerkeleyGW with following replacement: vcoul(:)=coulfact/(8.0d0 * PI_D)
Also: zero out exchange contribution in shiftenergies_dyn

to include the core density:
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i) run opium and plot density (e.g. ./opium Pd.param log all plot den)
ii) the file Pd.pcc_plt contains core and valence densities

steps to calculating spin susceptibility


- calculate epsilon using BGW + use write_vcoul