ribbon.spiralshapes module

Functions to construct shapes based on plane spirals.

ribbon.spiralshapes.write_xyz(x, y, z, atom_symbol='C', filename='out.xyz', title='')

Writes atom positions to a XYZ file.

Parameters:

x, y, z1D array_like

x, y, and z coordinates of the atoms. All three must have the same length.

atom_symbolstr

Atom symbol. If more than two characters, will be trucated to the first two characters.

filenamepath_like

Name of output file (XYZ format) with extension ‘.xyz’.

titlestr

A title string for the XYZ file.

Returns:

None

ribbon.spiralshapes.extrude(xcoords, ycoords, zdist, dz)

Creates a sheet of monoatomic thickness by extruding a spiral and returns the positions of the atoms of the sheet.

Parameters:

xcoords, ycoords1D array_like

X & Y coordinates of the points on the planar curve.

zdistfloat

Extrusion distance (along z-direction)

dzfloat

Spacing along the z-direction

Returns:

X, Y, Ztuple of 1D ndarrays

Coordinates of the atoms of the sheet.

ribbon.spiralshapes.double_spiral(spiral, L, ds=0.5, same=False, end=1, f=0.0)

Create a double spiral from a single spiral.

The two spirals may be joined at either of the two ends. In addition, before joining, a the curvature of fraction of the arclength of both spirals may be linearized (if f > 0). Linearization is done by replacing a length fL of the curve by a Cornu spiral, whose curvature varies linearly with arclength, such that there is no discontinuity in the curvature of the resulting double spiral.

Parameters:

spiralSpiralPolarBase | SpiralCartesianBase

A spiral object

Lfloat

Arclength of spiral. The double spiral will have arclength 2L.

dsfloat

Spacing along the arclength.

samebool

Whether the spirals are on the same side or not.

end{0, 1}

If 0, the s=0 end. If 1, the s=L end.

ffloat

Fraction of the arclength L over which the curvature will be linearized.

Returns:

s_ds, kappa_ds, x_ds, y_dstuple of 1D ndarrays

The arclength coordinates (s_ds), curvatures (kappa_ds), x-coordinates (x_ds), and y-coordinates (y_ds) of the double spiral.

Warning

• Linearization may not always be necessary, and in some cases may lead to significant changes in the derivative of the curvature along the arclength.

• Depending on the parameters of the spiral and which end is chosen for joining, the double spiral may self-intersect.