Scissor correction in Epsilon and Sigma

[Hong]

Dear BGW masters,

Questions are 

1. I thought BGW usually calculate RPA epsilon,  the chi_0 is usually calculated from KS DFT orbitals, it seems do not need quasiparticle energies. So do not need so-called scissor correction. Right?  Why in manual, I saw there are scissor correction parameters in epsilon.inp? 

2. Sigma calculations are for quasiparticle energies: eqp0.dat and eqp1.dat, the latter is really used. Can we do scissor corrections here directly from KS mean field energies to get "  eqp0.dat and eqp1.dat" without calculating self-energy sigma?  If so, please let us know how to do it. 

Looking forward to your help.

Best,

Hong

   

   

[Brad Barker]

Hello Hong,

1. It is an option to use scissors parameters for the calculation of chi_0, but in almost any circumstance the best option is to use the KS bands and energies.

2. The scissors parameters are determined from an initial one-shot "G_0 W_0" calculation of the self-energy matrix elements, and finding a linear fit for the valence and conduction bands near the Fermi level. You would then use a scissors operator to update calculations of self-energy matrix elements for "eigenvalue self-consistency." (Better solution to Dyson's Equation, for a given set of bands.)

Are you interested in self-consistent GW? For many materials, one-shot G_0 W_0 is sufficient.

Best,
Bradford A. Barker

Postdoctoral scholar, Strubbe Ab Initio Laboratory
UC Merced

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[Hong Tang]

Hi Brad,

Thank you so much for helping.

It looks that those scissor corrections are for the purpose of self-consistent GW. 

The scissor in epsilon is for updating W, and the scissor in sigma is for updating G, aren't they? 

Best,

Hong

 

---

From: Brad Barker <brad.barke...@gmail.com>
Sent: Thursday, August 5, 2021 2:17 PM
To: Hong Tang <hong.t...@temple.edu>
Cc: BerkeleyGW Help <he...@berkeleygw.org>
Subject: [External] Re: Scissor correction in Epsilon and Sigma

 

[Brad Barker]

Hi Hong,

The scissor in Sigma technically corrects the band energies in the denominator for the matrix elements of the self-energy. See, for example, equations 19 through 22 in https://arxiv.org/abs/1111.4429 .

Best,
Brad Barker

UC Merced