This is an example of input file to be given to EXC. For a complete list of input variables see below.


exciton ! important

exc ! full excitonic calculation. this will imply the use of an abinit SCR file

so ! use a scissor operator which implies a value for soenergy,
! alternatively you might use 'gw' which implies the use of an abinit GW file
soenergy 0.6

shiftk ! put this value if you use shifted k-points

matsh 4 ! this is just an update of the old (still working) npwmat
(but instead of giving the total number of plane waves, you give a closed shell)
npwsh 12 ! this is just an update of the old (still working) npwwfn
(but instead of giving the total number of plane waves, you give a closed shell)

nband 8 ! last band to be considered in the calculation
lomo 1 ! first band to be considered: 1 is default

haydock ! use haydock iterative technique: this avoid the full diagonization
niter 100 ! number of iterations in the haydock iterative scheme

omegai 0.0 ! first frequency (eV)
omegae 10.0 ! last frequency (eV)
domega 0.1 ! step of frequency (eV)
broad 0.1 ! Lorentzian broadening (eV)

q 0. 0. 0. ! momentum transfer: (0,0,0) is default, like for optical regime

savememory ! permits to save a little memory
verboselevel 1 ! this is the default. a value of 3 will print out lots of stuff


!----- Type of calculation (default: linear response:tddft) -------------------
linear ! default: linear response in G space.
! solving the tddft equation for \chi
! this is not implemented in EXC

exciton ! excitonic calculation (the EXC code) in transition space
!--------------------------------------------------------------------------------

!---------- Energies for the diagonal part of H^exc (default:enks) ---------------------------------
enks ! default: use the Kohn-Sham eigenvalues found in the ground-state file
! to construct the diagonal of H^exc
gw ! perturbative GW energies: this variable implies the existence of a gwfile
qpsenergy ! self-consistent quasiparticle energies. this variable implies the
! existence of a qps file
so ! scissor operator correction.
! see below soenergy, stretch_valence, stretch_conduction
soenergy ! value of the scissor correction. default: 0.0
stretch_valence ! stretch = GW bandwidth / DFT bandwidth. default: 1.0
stretch_conduction ! modify energy in a linear way in order to reproduce the GW bandwidth
! like: e_GW = e_DFT * stretch
somult ! multi-scissor operator correction. implies the existence of a file
! called somult.in
!---------------------------------------------------------------------------------------------------

!---------- Wavefunctions for the matrix elements (default:kss) ----------------------------
kss ! default. use the Kohn-Sham wavefunctions found in the ground-state file
! to construct the numerator of \chi^0
qps ! self-consistent quasiparticle eavefunctions. this variable implies the existence
! of a qps file
!-------------------------------------------------------------------------------------------

!------ Tamm-Dancoff Approximation (default) ---------------------------------------------------------
tammdancoff ! if this flag occurs the calculation will use the so-called Tamm-Dancoff approximation,
! i.e. only the resonant part of H^exc will be taken into account
resonant ! equivalent to tammdancoff
!-----------------------------------------------------------------------------------------------------

!--- Exciton solver (default:fulldiago) --------------------------------------------------------------
fulldiago ! default. diagonalization of the excitonic hamiltonian.
haydock ! iterative inversion of the excitonic hamiltonian. implies the variable niter (see below).
! only the final spectrum is obtained but no excitonic eigenvalues and eigenvectors,
! preventing further analysis.
niter ! number of iterations for the haydock iterative procedure. default:100
haydock_restart ! write restart file. default false
!-----------------------------------------------------------------------------------------------------

!---- Screening --------------------------------------------------------------------------
wdiag ! default: only the diagonal (in G) of Wgg' is retained. it turns out to be a good
! approximation for solids
wfull !the whole gg' structure of W is used. important for clusters.

lf ! default: calculate also the exchange term <>.
nlf ! avoid the calculation of the exchange term <>. if rpa this corresponds to
! to a calculation without local fields.
!------------------------------------------------------------------------------------------

!----- Use of shikted k-points --------------------------------------------------
shiftk ! if the ground state structure has been calculated using shifted
! k-points, we have to tell dp about it, otherwise it will try to use
! the symmetries of the system to sample the whole Brillouin zone.
! Alternatively (and deprecatively) you can still use the old way ...
nsymk 1 ! force EXC to consider only the first symmetry (the identity)
noinvk ! do not use inversion
! Remember: either one uses the 'shiftk' flag OR 'nsym 1' + 'noinv'
!--------------------------------------------------------------------------------

!----- convergency parameters ----------------------------------------------------
npwwfn ! number of plane waves to describe the wavefunctions
! default: all plane waves found on the _KSS file will be used
wfnsh ! number of shells of plane waves to describe the wavefunctions
! default:all
! Remark: only one of the above parameters has to be specified

npwmat ! number of G-vectors for the \epsilon matrix (related to local
! fields) ! default:all
matsh ! number of shells og G-vectors for the \epsilon matrix (related
! to local fields) ! default:all
! Remark: only one of the above parameters has to be specified

nbands ! number of the last band (highest energy) to be included in the
! calculation ! default:all
lomo ! number of the first band (lowest energy) to be included in the
! calculation ! default:1
!---------------------------------------------------------------------------------

!-- Pseudopotential --------------------------------------------------------------
novkb ! exclude the nonlocal part of the pseudopotential, which is unfortunately
! the leading term for a big number of transitions
!---------------------------------------------------------------------------------

!----- Momentum Transfer - Polarization of light ---------------------------------
q
! This specifies the momentun transfer (vector) to the
! system. The value of q can range from 0 to very high
! value (several Brilloun zones equivalent)
! Very high q vector can be found in Electron energy loss
! or Inelastic X-ray Scattering. The case q=0 is
! particularly important for optical absorption, where the
! polarization of light can be secified giving a small
! value in one or another direction, e.g.
! q 0.0001 0.0001 0.0
! Remark: q uses the reduced coordinates here, not the
! cartesian ones.
doublegrid ! Allows to read two separate KSS-files for initial and final
! states, which are shifted by q with respect to each other.
! (e.g. k.p perturbation theory will be avoided at small q)
! USAGE: dp -i -k -k
! dp1.kss corresponds to the final states at k,
! dp2.kss corresponds to the initial states at k-q
antieps ! calculation of eps*(-q,-w) instead of eps(q,w), which
! corresponds to exchanging the two kss files in doublegrid
!---------------------------------------------------------------------------------

!----- Other flags -----------------------------------------------------------------
savememory ! if present this flag will make the code calculating the rhotw
! at any transition with a double Fourier transform, rather than
! storing the wave functions in real space. Advantage: reduction
! of the memory. Disadvantage: 3 instead of 2 Fourier
! transform per wavefunction.
verboselevel ! =0,1,2,3
! 0) minimum amount of info written down
! 1) default values. essential things are written down
! 2) Verbose mode: many more things are written down
! 3) Debug mode: to use only in debugging case,
! all the loop indices are written
! (tree and mem files created)
!-----------------------------------------------------------------------------------