Epsilon
code input keywords (epsilon.inp
)
Required keywords
Optional keywords
broadening [float]
cell_box_truncation
cell_slab_truncation
cell_wire_truncation
coulomb_truncation_radius [float]
cvfit [array of integers]
degeneracy_check_override
delta_frequency [float]
delta_frequency_step [float]
delta_sfrequency [float]
delta_sfrequency_step [float]
dont_use_hdf5
ec0 [float]
ecdel [float]
ecs [float]
eqp_corrections
ev0 [float]
evdel [float]
evs [float]
fermi_level [float]
fermi_level_absolute
fermi_level_relative
frequency_dependence [integer]
frequency_dependence_method [integer]
frequency_high_cutoff [float]
frequency_low_cutoff [float]
full_chi_conv_log [integer]
fullbz_replace
fullbz_write
gcomm_elements
gcomm_matrix
imaginary_frequency [float]
init_frequency [float]
nfreq_group [integer]
no_min_fftgrid
number_bands [integer]
number_imaginary_freqs [integer]
number_valence_pools [integer]
plasma_freq [float]
qgrid [array of integers]
restart
sfrequency_high_cutoff [float]
sfrequency_low_cutoff [float]
skip_chi
skip_epsilon
spherical_truncation
subsample
verbosity [integer]
write_vcoul
Keyword documentation
Parameters for fullfrequencydependent calculations
Three methods are available, depending on the value of frequency_dependence_method
:

0: Realaxis formalism with AdlerWiser formula:
 A uniform frequency grid is set up from
init_frequency
(defaults to 0), up tolow_frequency_cutoff
, with a spacing ofdelta_frequency
between two frequencies.  A nonuniform frequency grid is setup from
low_frequency_cutoff
tohigh_frequency_cutoff
, where the frequency spacing gets increased bydelta_frequency_step
.
 A uniform frequency grid is set up from

1: Realaxis formalism with spectral method:
 A uniform frequency grid is set up from
init_frequency
(defaults to 0), up tolow_frequency_cutoff
, with a spacing ofdelta_frequency
between two frequencies.  A nonuniform frequency grid is setup from
low_frequency_cutoff
tohigh_frequency_cutoff
, where the frequency spacing gets increased bydelta_frequency_step
.  A separate frequency grid is setup for the spectral function. The variables
init_sfrequency
,delta_sfrequency
,delta_sfrequency_step
,sfrequency_low_cutoff
, andsfrequency_high_cutoff
define this grid, in an analogy to the flags used to define the grid for the polarizability matrix.
 A uniform frequency grid is set up from

2: Contourdeformation formalism with AdlerWiser formula (default).

A uniform frequency grid is set up from
init_frequency
(defaults to 0), up tolow_frequency_cutoff
, with a spacing ofdelta_frequency
between two frequencies.  A frequency grid with
number_imaginary_freqs
is setup on the imag axis.
frequency_dependence_method [integer]
Full frequency dependence method for the polarizability, if frequency_dependence
==2:
 0: Realaxis formalism, AdlerWiser formula.
 1: Realaxis formalism, spectral method (PRB 74, 035101, (2006))
 2: Contourdeformation formalism, AdlerWiser formula.
broadening [float]
Broadening parameter for each val>cond transition. It should correspond to the energy resolution due to kpoint sampling, or a number as small as possible if you have a molecule. The default value is 0.1 for method 0 and 1, and 0.25 for method 2.
init_frequency [float]
Lower bound for the linear frequency grid.
frequency_low_cutoff [float]
Upper bound for the linear frequency grid. For methods 0 and 1, it is also the lower bound for the nonuniform frequency grid. Should be larger than the maximum transition, i.e., the energy difference between the highest conduction band and the lowest valence band. The default is 200 eV for method 0 and 1, and 10 eV for method 2. For method 2, you can increase frequency_low_cutoff if you wish to use the Sigma code and look into QP states deep in occupied manifold or high in the unoccupied manifold.
delta_frequency [float]
Frequency step for fullfrequency integration for the linear grid Should be converged (the smaller, the better). For molecules, delta_frequency should be the same as broadening. Defaults to the value of broadening.
number_imaginary_freqs [integer]
Number of frequencies on the imaginary axis for method 2.
frequency_high_cutoff [float]
Upper limit of the nonuniform frequency grid.
Defaults to 4*frequency_low_cutoff
delta_frequency_step [float]
Increase in the frequency step for the nonuniform frequency grid.
delta_sfrequency [float]
Frequency step for the linear grid for the spectral function method.
Defaults to delta_frequency
.
delta_sfrequency_step [float]
Increase in frequency step for the nonuniform grid for the spectral function method.
Defaults to delta_frequency_step
sfrequency_low_cutoff [float]
Upper bound for the linear grid for the spectral function method
and lower bound for the nonuniform frequency grid.
Defaults to frequency_low_cutoff
sfrequency_high_cutoff [float]
Upper limit of the nonuniform frequency grid for the spectral function method.
Defaults to frequency_low_cutoff
Scissors operator
Scissors operator (linear fit of the quasiparticle
energy corrections) for the bands in WFN
and WFNq
.
For valenceband energies:
ev_cor = ev_in + evs + evdel * (ev_in  ev0)
For conductionband energies:
ec_cor = ec_in + ecs + ecdel * (ec_in  ec0)
Defaults is zero for all entries, i.e., no scissors corrections.
evs
, ev0
, ecs
, ec0
are in eV.
If you have eqp.dat
and eqp_q.dat
files
this information is ignored in favor of the eigenvalues
in eqp.dat and eqp_q.dat.
One can specify all parameters for scissors operator
in a single line with cvfit evs ev0 evdel ecs ec0 ecdel
evs [float]
ev0 [float]
evdel [float]
ecs [float]
ec0 [float]
ecdel [float]
cvfit [array of integers]
Truncation schemes for the Coulomb potential
Since BerkerleyGW is a planewavebased code, one must truncate the Coulomb potential to avoid spurious interactions between repeated supercells when dealing with systems with reduced dimensionality. Make sure you understand how to setup your meanfield calculation so that the supercell is large enough to perform a truncation of the Coulomb potential.
cell_box_truncation
Truncate the Coulomb potential based on the WignerSeitz cell. This is the recommended truncation for 0D systems.
cell_wire_truncation
Truncation scheme for 1D systems, such as carbon nanotubes. The z direction is assumed to be periodic, and x and y confined.
cell_slab_truncation
Truncation scheme for 2D systems, such as graphene or monolayer MoS2. The z direction is assumed to be confined, and x and y periodic.
spherical_truncation
Truncate the Coulomb potential based on an analytical scheme.
This is ok for quasispherical systems, such as CH4 molecule or C60,
but the cell_box_truncation
is the most general and recommended
scheme. When using spherical truncation, you must also specify the
radius for the truncation in spherical_truncation
.
coulomb_truncation_radius [float]
This specifies the radius of for spherical truncation, in Bohr,
so that the Coulomb potential v(r) is zero for r larger than
these values. This flag is to be used together with spherical_truncation
.
Misc. parameters
epsilon_cutoff [float]
Energy cutoff for the dielectric matrix, in Ry. The dielectric matrix \varepsilon_{GG'} will contain all Gvectors with kinetic energy q+G^2 up to this cutoff.
number_bands [integer]
Total number of bands (valence+conduction) to sum over. Defaults to the number of bands in the WFN file minus 1.
frequency_dependence [integer]
This flags specifies the frequency dependence of the inverse dielectric matrix:
 Set to 0 to compute the static inverse dielectric matrix (default).
 Set to 2 to compute the full frequency dependent inverse dielectric matrix.
 Set to 3 to compute the two frequencies needed for GodbyNeeds GPP model.
plasma_freq [float]
Plasma frequency (eV) needed for the contourdeformation method (i.e.,
frequency_dependence
==2). The exact value
is unimportant, especially if you have enough imaginary frequency points. We
recommend you keep this value fixed at 2 Ry.
imaginary_frequency [float]
For frequency_dependence
==3, the value of the purely imaginary frequency, in eV:
full_chi_conv_log [integer]
Logging convergence of the head & tail of polarizability matrix with respect to conduction bands:
 Set to 1 for no convergence test
 Set to 0 for the 5 column format including the extrapolated values (default).
 Set to 1 for the 2 column format, real part only.
 Set to 2 for the 2 column format, real and imaginary parts.
begin qpoints ... end
qx qy qz 1/scale_factor is_q0
scale_factor is for specifying values such as 1/3
is_q0 = 0 for regular, nonzero qvectors (read val WFNs from WFN
)
is_q0 = 1 for a small qvector in semiconductors (read val WFNs from WFNq
)
is_q0 = 2 for a small qvector in metals (read val WFNs from WFN
)
if present the small qvector should be first in the list
You can generate this list with kgrid.x
: just set the shifts to zero and use
same grid numbers as for WFN
. Then replace the zero vector with q0.
fermi_level [float]
Specify the Fermi level (in eV), if you want implicit doping
Note that value refers to energies after scissor shift or eqp corrections.
See also fermi_level_absolute
and fermi_level_relative
to control
the meaning of the Fermi level.
The Fermi level in keyword fermi_level
can be treated as an absolute
value or relative to that found from the mean field (default)
fermi_level_absolute
fermi_level_relative
dont_use_hdf5
Read from traditional simple binary format for epsmat/eps0mat instead of HDF5 file format. Relevant only if code is compiled with HDF5 support.
verbosity [integer]
Verbosity level, options are:
 1: default
 2: medium  info about kpoints, symmetries, and eqp corrections.
 3: high  full dump of the reduced and unfolded kpoints.
 4: log  log of various function calls. Use to debug code.
 5: debug  extra debug statements. Use to debug code.
 6: max  only use if instructed to, severe performance downgrade. Note that verbosity levels are cumulative. Most users will want to stick with level 1 and, at most, level 3. Only use level 4+ if debugging the code.
eqp_corrections
Set this to use eigenvalues in eqp.dat and eqp_q.dat If not set, these files will be ignored.
write_vcoul
Write the bare Coulomb potential v(q+G) to file
Matrix Element Communication Method (Chi Sum Comm). Default is gcomm_matrix
which is good if nk, nc, nv > nmtx, nfreq. If nk, nc, nv < nfreq, nmtx
(nk, nv < nfreq since nc \sim nmtx), use gcomm_elements. Only gcomm_elements
is supported with the spectral method.
gcomm_matrix
gcomm_elements
number_valence_pools [integer]
Number of pools for distribution of valence bands The default is chosen to minimize memory in calculation
By default, the code computes the polarizability matrix, constructs the dielectric matrix, inverts it and writes the result to file epsmat. Use keyword skip_epsilon to compute the polarizability matrix and write it to file chimat. Use keyword skip_chi to read the polarizability matrix from file chimat, construct the dielectric matrix, invert it and write the result to file epsmat.
skip_epsilon
skip_chi
nfreq_group [integer]
(Full Frequency only) Calculates several frequencies in parallel. No "new"
processors are used here, the chi summation is simply done in another order
way to decrease communication. This also allows the inversion of multiple
dielectric matrices simultaneously via ScaLAPACK, circumventing ScaLAPACK's
scaling problems. Can be very efficient for system with lots of Gvectors and when
you have many frequencies. In general gives speedup. However, in order to
calculate N frequencies in parallel, the memory to store pol%gme
is currently
multiplied by N as well.
'unfolded BZ' is from the kpoints in the WFN file 'full BZ' is generated from the kgrid parameters in the WFN file See comments in Common/checkbz.f90 for more details
fullbz_replace
Replace unfolded BZ with full BZ
fullbz_write
Write unfolded BZ and full BZ to files
degeneracy_check_override
The requested number of bands cannot break degenerate subspace Use the following keyword to suppress this check Note that you must still provide one more band in wavefunction file in order to assess degeneracy
no_min_fftgrid
Instead of using the RHO FFT box to perform convolutions, we automatically determine (and use) the smallest box that is compatible with your epsilon cutoff. This also reduces the amount of memory needed for the FFTs. Although this optimization is safe, you can disable it by uncommenting the following line:
restart
Use this flag if you would like to restart your Epsilon calculation instead of starting it from scratch. Note that we can only reuse qpoints that were fully calculated. This flag is ignored unless you are running the code with HDF5.
qgrid [array of integers]
Qgrid for the epsmat file. Defaults to the WFN kgrid.
subsample
Use this option to generate an eps0mat file suitable for subsampled Sigma calculations. The only thing this flag does is to allow a calculation with more than one q\rightarrow0 points without complaining.