def _bands_from_force_constants(data: ForceConstants,
q_distance: Quantity,
insert_gamma: bool = True,
frequencies_only: bool = False,
**calc_modes_kwargs
) -> Tuple[Union[QpointPhononModes,
QpointFrequencies],
XTickLabels, SplitArgs]:
structure = data.crystal.to_spglib_cell()
bandpath = seekpath.get_explicit_k_path(
structure,
reference_distance=q_distance.to('1 / angstrom').magnitude)
if insert_gamma:
_insert_gamma(bandpath)
x_tick_labels = _get_tick_labels(bandpath)
split_args = {'indices': _get_break_points(bandpath)}
print(
"Computing phonon modes: {n_modes} modes across {n_qpts} q-points"
.format(n_modes=(data.crystal.n_atoms * 3),
n_qpts=len(bandpath["explicit_kpoints_rel"])))
qpts = bandpath["explicit_kpoints_rel"]
if frequencies_only:
modes = data.calculate_qpoint_frequencies(qpts,
reduce_qpts=False,
**calc_modes_kwargs)
else:
modes = data.calculate_qpoint_phonon_modes(qpts,
reduce_qpts=False,
**calc_modes_kwargs)
return modes, x_tick_labels, split_args
def sample_sphere_dos(fc: ForceConstants,
mod_q: Quantity,
sampling: str = 'golden',
npts: int = 1000, jitter: bool = False,
energy_bins: Quantity = None,
**calc_modes_args
) -> Spectrum1D:
"""Sample the phonon DOS, averaging over a sphere of constant |q|
Parameters
----------
fc
Force constant data for system
mod_q
radius of sphere from which vector q samples are taken (in units
of inverse length; usually 1/angstrom).
sampling
Sphere-sampling scheme. (Case-insensitive) options are:
- 'golden':
Fibonnaci-like sampling that steps regularly along one
spherical coordinate while making irrational steps in
the other
- 'sphere-projected-grid':
Regular 2-D square mesh projected onto sphere. npts will
be distributed as evenly as possible (i.e. using twice
as many 'longitude' as 'lattitude' lines), rounding up
if necessary.
- 'spherical-polar-grid':
Mesh over regular subdivisions in spherical polar
coordinates. npts will be rounded up as necessary in
the same scheme as for sphere-projected-grid. 'Latitude'
lines are evenly-spaced in z
- 'spherical-polar-improved':
npts distributed as regularly as possible using
spherical polar coordinates: 'latitude' lines are
evenly-spaced in z and points are distributed among
these rings to obtain most even spacing possible.
- 'random-sphere':
Points are distributed randomly in unit square and
projected onto sphere.
npts
Number of samples. Note that some sampling methods have
constraints on valid values and will round up as appropriate.
jitter
For non-random sampling schemes, apply an additional random
displacement to each point.
energy_bins
Preferred energy bin edges. If not provided, will setup
1000 bins (1001 bin edges) from 0 to 1.05 * [max energy]
**calc_modes_args
other keyword arguments (e.g. 'use_c') will be passed to
ForceConstants.calculate_qpoint_phonon_modes()
Returns
-------
Spectrum1D
"""
qpts_cart = _get_qpts_sphere(npts, sampling=sampling, jitter=jitter
) * mod_q
qpts_frac = _qpts_cart_to_frac(qpts_cart, fc.crystal)
phonons = fc.calculate_qpoint_frequencies(qpts_frac, **calc_modes_args
) # type: QpointFrequencies
if energy_bins is None:
energy_bins = _get_default_bins(phonons)
return phonons.calculate_dos(energy_bins)