how to make the Automatically detected repetitions suitable

[njuxyh]

i have a 1D nanoribbon, its periodic direction is along z, and the x and y, i creat supercell.

the cell size x:19 y:50 z:x angstrom.

but when i calculate the phonon bandstructure, the output is Automatically detected repetitions(3,1,7)

so, i enlarger the x cell size to 50, but the result is also (3,1,7)
 

there i do not know how to make the Automatically detected repetitions  to be (1,1,7)?

please help me!

thanks very much!

[kstokbro]

Set the dynamical_matrix_parameters, i.e.
dynamical_matrix_parameters = DynamicalMatrixParameters(
    repeats=(1,1,7),
    atomic_displacement=0.01*Ang
    )
calculator = LCAOCalculator(
    dynamical_matrix_parameters=dynamical_matrix_parameters)