# RTBSE

Controls options for the real-time Bethe-Salpeter (RTBSE) propagation. Note that running RTBSE requires previous low-scaling GW calculation. Also note that designating this section as RTBSE run but choosing run type ENERGY leads to potential deallocation errors. [Edit on GitHub]

Subsections

- PADE_FT

## Keywords

- SECTION_PARAMETERS

- FT_DAMPING

- FT_START_TIME

- RTBSE_HAMILTONIAN

## Keyword descriptions

SECTION_PARAMETERS: enum = TDDFT

  Lone keyword: `RTBSE`

  Usage: &RTBSE TDDFT

  Valid values:

  - `TDDFT` Use TDDFT for density matrix/MO propagation.

  - `RTBSE` Use RT-BSE for Green’s function propagation

  Mentions: ⭐Real-Time Bethe-Salpeter Propagation

  Which method is used for the time propagation of electronic structure. By default, use the TDDFT method. Can also choose RT-BSE method, which propagates the lesser Green’s function instead of density matrix/molecular orbitals. [Edit on GitHub]

FT_DAMPING: real = -1.00000000E+000 [fs]

  Mentions: ⭐Real-Time Bethe-Salpeter Propagation

  Numerical Fourier transform (required for calculation of MOMENTS_FT and POLARIZABILITY) can oscillate when the final values are far away from zero. This keyword controls the exponential damping in the Fourier transform (Fourier transform is used for calculation of MOMENTS_FT and POLARIZABILITY). For negative values (the default), calculates the damping at the run time so that the last point in the time trace is reduced by factor e^(-4). When set manually, determines the time in which the moments trace is reduced by factor of e^(-1), except when set to zero, in which case the damping is not applied. [Edit on GitHub]

FT_START_TIME: real = 0.00000000E+000 [fs]

  Mentions: ⭐Real-Time Bethe-Salpeter Propagation

  The starting time from which damping is applied and from which on the trace is considered for the Fourier transform (Fourier transform is used for the calculation of MOMENTS_FT and POLARIZABILITY). Useful for real-time pulse - one can specify the center of the pulse as the starting point. [Edit on GitHub]

RTBSE_HAMILTONIAN: enum = G0W0

  Usage: RTBSE_HAMILTONIAN G0W0

  Valid values:

  - `KS` Use Kohn-Sham Hamiltonian for Green’s propagation.

  - `G0W0` Use G0W0 Hamiltonian for Green’s function propagation

  Which Hamiltonian to use as the single-particle Hamiltonian in the Green’s propagator. [Edit on GitHub]