SAPO
code overview
Warning
The SAPO documentation is under development!
The SAPO (Simple Approximate Physical Orbitals) code reads DFT wavefunctions from WFN file, generates additional wavefunctions on top of them, and writes both to another WFN file. It can generate plane waves, decompose them into irreducible representations of the space group of the Bravais lattice or the crystal, and orthonormalize them with respect to DFT wavefunctions. It can insert SIESTA wavefunctions read from auxiliary WFN file in between plane waves and orthonormalize them altogether. It can apply a random variation to the plane waves and SIESTA wavefunctions or generate completely random wavefunctions and orthonormalize them. It can correct eigenvalues during orthonormalization or perform subspace diagonalization. It can drop the plane waves and SIESTA wavefunctions which have a large overlap with DFT wavefunctions. It can keep wavefunctions with the eigenvalues in a given energy range. It can extract eigenvalues and plane wave coefficients from WFN file for plotting purposes.
The SAPO method is described in Phys. Rev. Lett. 107, 186404 (2011).
A few notes:

When using iterative Davidson diagonalization, it is recommended to generate
VXC
rather thanvxc.dat
inpw2bgw
run, then compute matrix elements ofVXC
betweenSAPO
wavefunctions. This is more consistent than usingvxc.dat
becausevxc.dat
is computed between ESPRESSO wavefunctions, and those might be slightly different fromSAPO
wavefunctions. 
wfng_input_file
should contain all occupied orbitals (and may or may not contain some unoccupied orbitals), otherwise occupations written towfng_output_file
will be wrong. 
Symmetrization of planewaves (
sapo_symmetry .gt. 0
) has no effect on a SAPO calculation since it is just a linear combination in a degenerate subspace. It is currently disabled because it requires symmetry subroutines from Quantum ESPRESSO which are not compatible with our BSDtype license. To enable it: openMeanField/SAPO/pw.f90
; comment outdie
; uncomment calls tos_axis_to_cart
,find_group
,set_irr_rap
, anddivide_class
; and link the corresponding routines from Quantum ESPRESSO.
SAPO
input file (sapo.inp
)
Below is a typical example of a SAPO
input file, sapo.inp
:
&input_sapo wfng_input_file = 'wfng.in' wfng_aux_file = '' vlr_input_file = '' vnlg_input_file = '' wfng_output_file = 'wfng.out' sapo_band_number = 0 sapo_planewave_min = 1 sapo_planewave_max = 580 sapo_energy_shift = 0.0 sapo_energy_match = .true. sapo_symmetry = 2 sapo_print_ir = .true. aux_flag = .false. aux_band_min = 0 aux_band_max = 0 aux_energy_shift = 0.0 sapo_random = 1 sapo_random_ampl = 1.0d3 sapo_overlap_flag = .false. sapo_overlap_max = 0.0 sapo_orthonormal = .true. sapo_ortho_block = 0 sapo_ortho_order = 0 sapo_ortho_energy = .false. sapo_energy_sort = .false. sapo_hamiltonian = .false. sapo_energy_range = .false. sapo_energy_min = 0.0 sapo_energy_max = 0.0 sapo_check_norm = .false. sapo_plot_kpoint = 0 sapo_plot_spin = 0 sapo_plot_bandmin = 0 sapo_plot_bandmax = 0 sapo_plot_pwmin = 0 sapo_plot_pwmax = 0 sapo_eigenvalue = .false. sapo_projection = 0 sapo_amplitude = .false. sapo_ampl_num = 0 sapo_ampl_del = 0.0 sapo_ampl_brd = 0.0 /
In this example, the wavefunctions are read from wfng.in
file and written to
wfng.out
file. The parameter sapo_band_number
specifies the number of
wavefunctions to be read from the input file (if set to 0 all the wavefunctions
will be read). The PW wavefunctions will be constructed from plane waves
ranging from 1 (sapo_planewave_min
) to 580 (sapo_planewave_max
). The
kinetic energies of the plane waves will be shifted to match the eigenvalues of
the input wavefunctions (sapo_energy_match
). The plane waves will be
decomposed into irreducible representations of the space group of the Bravais
lattice (sapo_symmetry = 2
), and the decomposition will be printed to the
standard output (sapo_print_ir
). The auxiliary wavefunctions will not be
inserted in between the PW wavefunctions (aux_flag
). A random variation
(sapo_random = 1
) with a small amplitude (sapo_random_ampl = 1.0d3
) will
be added to the PW wavefunctions. The PW wavefunctions will be orthonormalized
with respect to the valence and conduction bands (sapo_orthonormal
) in the
ascending order with respect to energy (sapo_ortho_order = 0
). The
orthonormality check will not be performed (sapo_check_norm
). The energy
eigenvalues, the projections of wavefunctions onto plane waves, and the squared
absolute values of amplitudes of the wavefunctions with respect to kinetic
energies of plane waves will not be plotted (sapo_eigenvalue
,
sapo_projection
, and sapo_amplitude
).
The auxiliary wavefunctions can be used in two different ways:

Use hybrid valence wavefunctions as
wfng_input_file
and LDA conduction wavefunctions aswfng_aux_file
, setsapo_planewave_min
andsapo_planewave_max
to 0,sapo_orthonormal
to.true
. andsapo_ortho_block
to 1. This way you will get a good starting point for nscf hybrid calculations in PARATEC or ESPRESSO. 
Use Siesta wrapper in
MeanField/SIESTA
directory to construct the resonant states from SIESTA wavefunctions (look intoMeanField/SIESTA/README
for details on how to usesiesta2bgw
), feed them to the SAPO code throughwfng_aux_file
parameter, and generate continuum states from plane waves by settingsapo_planewave_max
to a large number. Also setsapo_orthonormal
,sapo_ortho_block
andsapo_ortho_order
to orthonormalize the resonant and continuum states in the desired order with respect to the bound states from PARATEC or ESPRESSO. You may want to setsapo_ortho_energy
to.true.
for correcting the eigenvalues during the orthonormalization, or to setsapo_hamiltonian
to.true.
for correcting both the wavefunctions and the eigenvalues by diagonalizing the Hamiltonian. The latter requires the local potential file in Gaussian Cube format (vlr_input_file
), and optionally the nonlocal pseudopotential file (vnlg_input_file
). Finally, setsapo_energy_sort
to.true.
for sorting the resonant and continuum states by their eigenvalues before writing them to the output file. You may also setsapo_energy_range
to.true.
for keeping the eigenvalues in the energy range ofsapo_energy_min
tosapo_energy_max
.
Hint
If you don't know or don't want to manually set sapo_planewave_min
and
aux_band_min
, set both of them to 1, sapo_overlap_flag
to .true.
, and
sapo_overlap_max
to 0.3. This will automatically throw away
planewaves and auxiliary states that have large overlaps (scalar
products > 0.3) with DFT states and among themselves. The scalar
products of PW and AUX states with DFT states will be written to files
overlap_dft_k#_s#.dat
, and the scalar products of PW states with AUX
states will be written to files overlap_aux_k#_s#.dat
, so you can
inspect what states were thrown away after the run.