Yambo Community Forum

Posted: **Thu Sep 26, 2024 3:43 pm**

Hi,

Basically I know how to find out dielectric function using IP RPA approximation (yambo -o c). However, I came to know about scissor shift. How can I apply the scissor shift in the IP RPA (for metal and semiconductor)? I have seen some questions in the forum related to this and found out that the "yambo -o c -V qp" might generate the input file related to the scissor shift. After generating input file, I am confused with some parameters (as follows). Should I only focus on XfnQPdb= "none" and untouched other parameters?
I have gone through the tutorial https://www.yambo-code.eu/wiki/index.ph ... Structures. Though it's not related to IP RPA, however, if I change the XfnQPdb= "none" to XfnQPdb= "E < GW_QP_database/ndb.QP", Is that OK?

Code: Select all

XfnQPdb= "none"                  # [EXTQP Xd] Database action
XfnQP_INTERP_NN= 1               # [EXTQP Xd] Interpolation neighbours (NN mode)
XfnQP_INTERP_shells= 20.00000    # [EXTQP Xd] Interpolation shells (BOLTZ mode)
XfnQP_DbGd_INTERP_mode= "NN"     # [EXTQP Xd] Interpolation DbGd mode
% XfnQP_E
 0.000000 | 1.000000 | 1.000000 |        # [EXTQP Xd] E parameters  (c/v) eV|adim|adim
%
XfnQP_Z= ( 1.000000 , 0.000000 )         # [EXTQP Xd] Z factor  (c/v)
XfnQP_Wv_E= 0.000000       eV    # [EXTQP Xd] W Energy reference  (valence)
% XfnQP_Wv
 0.000000 | 0.000000 | 0.000000 |        # [EXTQP Xd] W parameters  (valence) eV| 1|eV^-1
%
XfnQP_Wv_dos= 0.000000     eV    # [EXTQP Xd] W dos pre-factor  (valence)
XfnQP_Wc_E= 0.000000       eV    # [EXTQP Xd] W Energy reference  (conduction)
% XfnQP_Wc
 0.000000 | 0.000000 | 0.000000 |        # [EXTQP Xd] W parameters  (conduction) eV| 1 |eV^-1
%
XfnQP_Wc_dos= 0.000000     eV    # [EXTQP Xd] W dos pre-factor  (conduction)

Thank you so much in advance.

Best Regards
M J Hasan
PhD Student
Mechanical Engineering
University of Maine

Posted: **Fri Sep 27, 2024 8:38 am**

Dear M J Hasan,

XfnQPdb is meant to apply QP correction read from a previous calculated quasiparticle database (e.g. after a GW calculation).
If you want to apply a rigid shift (scissor) you need to use:

Code: Select all

% XfnQP_E
 0.000000 | 1.000000 | 1.000000 |        # [EXTQP Xd] E parameters  (c/v) eV|adim|adim
%

The first value (in eV) is the scissor value, the other two fields are used to apply a linear stretching to the conduction and valence band respectively (1 means no stretching) and a simple scissor is applied.

Best,

Daniele

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