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# sknano.structures.compute_R¶

sknano.structures.compute_R(*Ch, *, bond=None, length=False, **kwargs)[source][source]

Compute symmetry vector $$\mathbf{R} = (p, q)$$.

The symmetry vector is any lattice vector of the unfolded graphene layer that represents a symmetry operation of the nanotube. The symmetry vector $$\mathbf{R}$$ can be written as:

$\mathbf{R} = p\mathbf{a}_1 + q\mathbf{a}_2$

where $$p$$ and $$q$$ are integers. The symmetry vector represents a symmetry operation of the nanotube which arises as a screw translation, which is a combination of a rotation $$\psi$$ and translation $$\tau$$. The symmetry operation of the nanotube can be written as:

$R = (\psi|\tau)$
Parameters: *Ch : {tuple or ints} Either a 2-tuple of ints or 2 integers giving the chiral indices of the nanotube chiral vector $$\mathbf{C}_h = n\mathbf{a}_1 + m\mathbf{a}_2 = (n, m)$$. bond : float, optional Distance between nearest neighbor atoms (i.e., bond length). Must be in units of Å. Default value is the carbon-carbon bond length in graphite, approximately $$\mathrm{a}_{\mathrm{CC}} = 1.42$$ Å length : bool, optional If True, return $$|\mathbf{R}|$$. (p, q) : tuple 2-tuple of ints – components of $$\mathbf{R}$$. float Length of $$\mathbf{R}$$ ($$|\mathbf{R}|$$) if length is True in units of Å.