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import warnings
from dataclasses import dataclass
import numpy as np
spin_error = (
'The spin keyword is no longer supported. Please call the function '
'with the energies corresponding to the desired spins.')
_deprecated = object()
def get_band_gap(calc, direct=False, spin=_deprecated):
warnings.warn('Please use ase.dft.bandgap.bandgap() instead!')
gap, (s1, k1, _n1), (s2, k2, _n2) = bandgap(calc, direct, spin=spin)
ns = calc.get_number_of_spins()
if ns == 2:
return gap, (s1, k1), (s2, k2)
return gap, k1, k2
@dataclass
class GapInfo:
eigenvalues: np.ndarray
def __post_init__(self):
self._gapinfo = _bandgap(self.eigenvalues, direct=False)
self._direct_gapinfo = _bandgap(self.eigenvalues, direct=True)
@classmethod
def fromcalc(cls, calc):
kpts = calc.get_ibz_k_points()
nk = len(kpts)
ns = calc.get_number_of_spins()
eigenvalues = np.array([[calc.get_eigenvalues(kpt=k, spin=s)
for k in range(nk)]
for s in range(ns)])
efermi = calc.get_fermi_level()
return cls(eigenvalues - efermi)
def gap(self):
return self._gapinfo
def direct_gap(self):
return self._direct_gapinfo
@property
def is_metallic(self) -> bool:
return self._gapinfo[0] == 0.0
@property
def gap_is_direct(self) -> bool:
"""Whether the direct and indirect gaps are the same transition."""
return self._gapinfo[1:] == self._direct_gapinfo[1:]
def description(self, *, ibz_kpoints=None) -> str:
"""Return human-friendly description of direct/indirect gap.
If ibz_k_points are given, coordinates are printed as well."""
from typing import List
lines: List[str] = []
add = lines.append
def skn(skn):
"""Convert k-point indices (s, k, n) to string."""
description = 's={}, k={}, n={}'.format(*skn)
if ibz_kpoints is not None:
coordtxt = '[{:.2f}, {:.2f}, {:.2f}]'.format(
*ibz_kpoints[skn[1]])
description = f'{description}, {coordtxt}'
return f'({description})'
gap, skn1, skn2 = self.gap()
direct_gap, skn_direct1, skn_direct2 = self.direct_gap()
if self.is_metallic:
add('No gap')
else:
add(f'Gap: {gap:.3f} eV')
add('Transition (v -> c):')
add(f' {skn(skn1)} -> {skn(skn2)}')
if self.gap_is_direct:
add('No difference between direct/indirect transitions')
else:
add('Direct/indirect transitions are different')
add(f'Direct gap: {direct_gap:.3f} eV')
if skn_direct1[0] == skn_direct2[0]:
add(f'Transition at: {skn(skn_direct1)}')
else:
transition = skn((f'{skn_direct1[0]}->{skn_direct2[0]}',
*skn_direct1[1:]))
add(f'Transition at: {transition}')
return '\n'.join(lines)
def bandgap(calc=None, direct=False, spin=_deprecated,
eigenvalues=None, efermi=None, output=None, kpts=None):
"""Calculates the band-gap.
Parameters:
calc: Calculator object
Electronic structure calculator object.
direct: bool
Calculate direct band-gap.
eigenvalues: ndarray of shape (nspin, nkpt, nband) or (nkpt, nband)
Eigenvalues.
efermi: float
Fermi level (defaults to 0.0).
Returns a (gap, p1, p2) tuple where p1 and p2 are tuples of indices of the
valence and conduction points (s, k, n).
Example:
>>> gap, p1, p2 = bandgap(silicon.calc)
>>> print(gap, p1, p2)
1.2 (0, 0, 3), (0, 5, 4)
>>> gap, p1, p2 = bandgap(silicon.calc, direct=True)
>>> print(gap, p1, p2)
3.4 (0, 0, 3), (0, 0, 4)
"""
if spin is not _deprecated:
raise RuntimeError(spin_error)
if calc:
kpts = calc.get_ibz_k_points()
nk = len(kpts)
ns = calc.get_number_of_spins()
eigenvalues = np.array([[calc.get_eigenvalues(kpt=k, spin=s)
for k in range(nk)]
for s in range(ns)])
if efermi is None:
efermi = calc.get_fermi_level()
efermi = efermi or 0.0
gapinfo = GapInfo(eigenvalues - efermi)
e_skn = gapinfo.eigenvalues
if eigenvalues.ndim == 2:
e_skn = e_skn[np.newaxis] # spinors
if not np.isfinite(e_skn).all():
raise ValueError('Bad eigenvalues!')
gap, (s1, k1, n1), (s2, k2, n2) = _bandgap(e_skn, direct)
if eigenvalues.ndim != 3:
p1 = (k1, n1)
p2 = (k2, n2)
else:
p1 = (s1, k1, n1)
p2 = (s2, k2, n2)
return gap, p1, p2
def _bandgap(e_skn, direct):
"""Helper function."""
ns, nk, nb = e_skn.shape
s1 = s2 = k1 = k2 = n1 = n2 = None
N_sk = (e_skn < 0.0).sum(2) # number of occupied bands
# Check for bands crossing the fermi-level
if ns == 1:
if np.ptp(N_sk[0]) > 0:
return 0.0, (None, None, None), (None, None, None)
else:
if (np.ptp(N_sk, axis=1) > 0).any():
return 0.0, (None, None, None), (None, None, None)
if (N_sk == 0).any() or (N_sk == nb).any():
raise ValueError('Too few bands!')
e_skn = np.array([[e_skn[s, k, N_sk[s, k] - 1:N_sk[s, k] + 1]
for k in range(nk)]
for s in range(ns)])
ev_sk = e_skn[:, :, 0] # valence band
ec_sk = e_skn[:, :, 1] # conduction band
if ns == 1:
s1 = 0
s2 = 0
gap, k1, k2 = find_gap(ev_sk[0], ec_sk[0], direct)
n1 = N_sk[0, 0] - 1
n2 = n1 + 1
return gap, (0, k1, n1), (0, k2, n2)
gap, k1, k2 = find_gap(ev_sk.ravel(), ec_sk.ravel(), direct)
if direct:
# Check also spin flips:
for s in [0, 1]:
g, k, _ = find_gap(ev_sk[s], ec_sk[1 - s], direct)
if g < gap:
gap = g
k1 = k + nk * s
k2 = k + nk * (1 - s)
if gap > 0.0:
s1, k1 = divmod(k1, nk)
s2, k2 = divmod(k2, nk)
n1 = N_sk[s1, k1] - 1
n2 = N_sk[s2, k2]
return gap, (s1, k1, n1), (s2, k2, n2)
return 0.0, (None, None, None), (None, None, None)
def find_gap(ev_k, ec_k, direct):
"""Helper function."""
if direct:
gap_k = ec_k - ev_k
k = gap_k.argmin()
return gap_k[k], k, k
kv = ev_k.argmax()
kc = ec_k.argmin()
return ec_k[kc] - ev_k[kv], kv, kc
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