class MonkhorstPackGrid(na=None, nb=None, nc=None, symmetries=None, force_timereversal=None, k_point_shift=None, shift_to_gamma=None)
  • na (Positive int) – Number of k-points in A direction.
    Default: 1
  • nb (Positive int) – Number of k-points in B direction.
    Default: 1
  • nc (Positive int) – Number of k-points in C direction.
    Default: 1
  • symmetries (list(n_symmetries) of (array(3, 3), array(3))) – A list of user-defined symmetries used for the reduction of the k-points in integration.
    Default: Empty list, which means ATK will determine the relevant symmetries.
  • force_timereversal (bool) – Always enforce time reversal symmetry.
    Default: True (False with spin-orbit or noncollinear spin)
  • k_point_shift (list(3) of float) – Optional k-point shift in fractional coordinates. This option is mutually exclusive to shift_to_gamma.
    Default: Determined internally depending on the value of shift_to_gamma.
  • shift_to_gamma (list(3) of bool | bool) – Shift grid so that \(\Gamma\) (0.0, 0.0, 0.0) is included along all or certain directions. This option is mutually exclusive to k_point_shift.
    Default: True (Not active if k_point_shift is specified)
Returns:All the k-points of the MonkhorstPackGrid before symmetry reduction.
Return type:ndarray(N,3) of float where N is the number of k-points.
Returns:The weight of all k-points before symmetry reduction.
Return type:ndarray(n) for float where n is the number of k-points before symmetry reduction.

After construction of the MonkhorstPackGrid, the time reversal symmetry can be disabled using this function.


Query method for getting the map between the symmetry reduced k-points and unreduced k-points.

Returns:A list with indices matching the k-points in the symmetry reduced set and in the unreduced set.
Return type:ndarray(N) with integer values between 0 and M-1. N is the number of k-points in the unreduced set, M is the number of k-points in the reduced set.
Returns:Whatever force_timereversal is enabled or disabled.
Return type:bool
Returns:The k_point_shift which the k-points are shifted with.
Return type:list(3) of float
Returns:The symmetry reduced kpoints.
Return type:ndarray(N,3) of float where N is the number of symmetry reduced k-points.
Returns:The weights of the symmetry reduced k-points.
Return type:ndarray(n) for floats, where n is the number of unreduced number of k-points.
Returns:The number of k-points along the kA-direction.
Return type:int
Returns:The number of k-points along the kB-direction.
Return type:int
Returns:The number of k-points along the kC-direction.
Return type:int
Returns:Whatever the k-points are shifted to the \(\Gamma\).
Return type:bool
Returns:The symmetries to apply for reducing the k-points.
Return type:list(n_symmetries) of (array(3, 3), array(3))

Usage Examples

Define a 2x5x3 Monkhorst-Pack k-point grid. Calculate the irreducible k-points using the time reversal symmetry and mirror symmetry in the A direction. Print out the relation between the full k-point set and the irreducible set:

# Make a  MonkhorstPackGrid with mirror symmetry in A direction and time reversal symmetry
symmetries = [( numpy.array([[-1,0,0], [0,1,0], [0,0,1]]), numpy.zeros(3))]
mpg = MonkhorstPackGrid(2, 5, 3, symmetries=symmetries)

# Get the kpoints
irreducible_kpoints = mpg.kpoints()
irreducible_weights = mpg.kpointsWeights()

all_kpoints = mpg.allKpoints()

# Print out the irreducible kpoints
print(len(irreducible_kpoints), ' irreducible kpoints')
for kp, w in zip(irreducible_kpoints, irreducible_weights):
    print(kp, w*len(all_kpoints))

# Get the map from the full kpoints to the irreducible part
fold_out_map = mpg.foldoutMapVector()

# Print out the relation between the full and irreducible set
print(len(all_kpoints), '  kpoints')
for i, kp in enumerate(all_kpoints):
    print(kp, ' -> ', irreducible_kpoints[fold_out_map[i]])


Make a uniform k-point grid according to procedure of Monkhorst and Pack [MP76],

\[\begin{split}&& {\bf k}_{prs} = u_{p}\, {\bf b}_{1} + u_{r}\, {\bf b}_{2} + u_{s}\, {\bf b}_{3}, \\ && u_{r} = (2 r - q - 1)/2q \,\,\,\,\,\,\,\,\, (r=1,2,3,...,q),\end{split}\]

where \({\bf k}_{prs}\) are the k-vectors corresponding to the special points of the k-grid, \({\bf b}_{1}\), \({\bf b}_{2}\), and \({\bf b}_{3}\) are the reciprocal lattice vectors, \(u_{r}\) is the sequence of numbers, and \(q^{3}\) is the total number of the k-points used to sample the Brillouin zone.

  • The original Monkhorst-Pack procedure assumes that odd k-point grids include the \(\Gamma\) point while even k-point grids avoid the \(\Gamma\) point.
  • It is possible and often advantageous to shift the grid by \(\Delta k\). For example, one may need to include the \(\Gamma\) point for cubic and hexagonal lattices.
  • When the time-reversal symmetry of the Schrödinger equation is preserved, it is possible to take advantage of the inversion symmetry to reduce the number of k-points used for sampling the Brillouin zone. This is done by default in QuantumATK.
  • If the time-reversal symmetry of the Schrödinger equation is broken, e.g., by spin-orbit interaction, the inversion symmetry cannot be adopted to reduce the number of k-points. The time-reversal symmetry can be turned off, by using the force_timereversal keyword.

[MP76]H. J. Monkhorst and J. D. Pack. Special points for brillouin-zone integrations. Phys. Rev. B, 13:5188–5192, Jun 1976. doi:10.1103/PhysRevB.13.5188.