Loading QP corrections

Databases from previous runs are automatically loaded loaded by simply pointing yambo to the folder which contains them. As an example, if a static screening calculation is performed,

$yambo -F screening.in -J em1s -C em1s

the static screening database ndb.em1s database is created and put inside the em1s folder. This can be later used in a bse run by setting

$yambo -F bse.in -J "bse,em1s" -C bse

The ndb.QP database is instead handled in a different way. It can be computed with a given SAVE folder, e.g. a SAVE folder generated with a given set of parameters, and later used with another SAVE folder generated with a different set of parameters. This is particularly useful when computing QP correction on a coarse k-points grid, and later using them on a finer kpt grid, for example for computing optical properties within BSE. As a consequence, the QP corrections computed with the yambo code are loaded by setting a dedicated variable in the input file

KfnQPdb= "E < 02_QP/ndb.QP uki"

The "uki" string controls the way in which the qp corrections are interpolated from the coarser to the finer grid. The default and means nearest kpt interpolation. However you can change it.

There are 4 available options:
- Number 4: Nearest K interpolation ("ui" or "uki") [default]
- Number 5: Nearest E interpolation ("uei")
- Number 6: Fourier K interpolation ("ubi")
- Number 7: Fit energie with shissor + stretching and use this to get the other values ("fit")

Options 4 and 6 can be reproduced by ypp. There are also two extra control options (that can be also found in ypp)

KfnQP_INTERP_NN= 1 [default] (number of NN considered, valid for 4)
KfnQP_INTERP_shells= XX (number of shells used, valid for 6 )