# SCREENING_IN_W

Screening \(\epsilon\) applied to \(W(\omega=0)=\epsilon^{-1}(\omega=0) v \) in the BSE calculation. Besides default BSE, i.e. \(W_0\) (screening with DFT energies), a fixed \(\alpha = \epsilon^{-1}(\omega)\) can be applied, which is similar to the mixing parameter for hybrid functionals in LR-TDDFT. In addition, the keywords TDHF (no screening - \(\alpha = 1\)) and RPA (infinite screening - \(\alpha = 0\)) can be applied. [Edit on GitHub]

## Keywords

- SECTION_PARAMETERS

- ALPHA

## Keyword descriptions

SECTION_PARAMETERS: enum = W_0

  Lone keyword: `W_0`

  Usage: &xc_functional BLYP

  Valid values:

  - `W_0` The Coulomb interaction is screened by applying DFT energies \(\varepsilon_p^{DFT}\), which is typically used for GW-BSE and often labeled as \(W_0\).

  - `TDHF` The Coulomb interaction is not screened, i.e. \(W_{pq,rs}(\omega=0) \rightarrow v_{pq,rs}\) enters.

  - `RPA` Infinite screening is applied, i.e. \(W_{pq,rs}(\omega=0) \rightarrow 0\).

  - `ALPHA` Arbitrary screening parameter. Specify within section.

  Shortcut for the most common functional combinations. [Edit on GitHub]

ALPHA: real = -1.00000000E+000

  Usage: ALPHA 0.25

  Screening parameter similar to the mixing in hybrid functionals used in TDDFT. \(\alpha\) mimicks the screening \(\epsilon^{-1}(\omega)\) and enforces \(W = \alpha v\) in the BSE calculation. [Edit on GitHub]