GW Interface

To calculate dielectric function, we need 2 wavefunctions from paratec. They are called CWFE and CWFEq. CWFE requires lots of conductance bands, but CWFEq only requires wavefunction of bands (valence bands + 2).

Procedure:
(1) Generate a converged charge density CD, save this CD to a file CD.conv. You must use the same charge density each time when you perform the following jobs.
(2) Compute CWFE. In the input file of paratec, use the options

number_bands 90 # this number means the number of conductance bands used in
outputflags gwr # the summation of dielectric function calculation

If the system does not have inversion symmetry, you need to run the complex version:

number_bands 90 # this is a large number compared to the number of valence bands
outputflags gwc

After run paratec, rename the file GWR (or GWC for complex version) to CWFE. You may need to use fewer or more bands in the option number_bands.

(3) Compute CWFEq. In the input file of paratec, use the options

number_bands 5         # this number is (number of valence bands + 2)
outputflags gwr        # use gwc if you want to run complex version of the GW code
gwshift 0.005 0.005 0.005

You should use number_bands slightly more than the number of valence bands in the system. gwshift gives a wavefuction at slightly shifted grid. Rename the file GWR to CWFEq after paratec computation.

GWC or GWR --> CWFE for the shifted grid (need many bands)
GWC or GWR --> CWFEq for slightly shifted+q grid (need only valence bands,need to read k-points from a file)

(4) Compute VXC and CD95. VXC is the information of exchange-correlation functional; CD95 is the charge density. In the input file of paratec, use the option

outputflags gwscreening

(5) Compute wfn0. In the input file of paratec, use the option

k_shift 0 0 0
number_bands 90        # test the convergence of this number
output_flags gwr       # use gwc if you want to run complex version of the GW code

Rename GWR or GWC to wfn0.

(6) Now you are ready to use CWFE and CWFEq to compute eps0mat and epsmat. eps0mat, epsmat, wfn0, VXC, CD95 are required to do GW calculation.