Once the executable `exc`

created (it should be in `\$prefix/bin`

after the make install) you can run the EXC code.

What you need is:

- The ground state calculation output =
`kss file`

. - GW corrected energy =
`gw file.`

- Screening function =
`em1 file.`

- An input file (see below)

Then execute: `exc -k file.kss -e file.em1 -g file.gw -i input > exc.log &`

Defaults:

The commmand `exc > exc.log &`

will look for a default `in.kss`

and `in.em1`

files in the current directory. An input file `exc.in`

will be also searched in the current directory.

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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

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!----- 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

stretch_valence

stretch_conduction

! 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

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 <

! 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

! default: all plane waves found on the _KSS file will be used

wfnsh

! default:all

! Remark: only one of the above parameters has to be specified

npwmat

! fields) ! default:all

matsh

! to local fields) ! default:all

! Remark: only one of the above parameters has to be specified

nbands

! calculation ! default:all

lomo

! 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

! 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

! 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) 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)

!-----------------------------------------------------------------------------------

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