File:BlochWaves1D.svg

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English: A Bloch wave (bottom) can be broken up into the product of a periodic function (top) and a plane-wave (center). Blue is real part, red is imaginary part. The left side and right side represent the same Bloch wave broken up in two different ways, involving the wave vector k1 (left) or k2 (right). The difference (k1-k2) is a reciprocal lattice vector.
Español: Una onda de Bloch (abajo) puede expresarse como el producto de una función periódica (arriba) y una onda plana (medio). La parte real es azul, y la parte imaginaria en rojo. Los lados izquierdo y derecho representan la misma onda de Bloch expresada de dos formas diferentes, involucrando los vectores de onda k1 (izquierda) o k2 (derecha). La diferencia (k1-k2) es un vector de la red recíproca.
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""" Steven Byrnes, 2013. This code is released to the public domain.  Written using Python 2.7, Matplotlib 1.2.1 """ from __future__ import division import math from math import pi import matplotlib.pyplot as plt import numpy as np  def u1(x):     """a funny looking function with period 1"""     fpart = math.modf(x)[0]     d = abs(fpart - 0.5)     return ((1j * math.cos(2 * pi * x + 2) + 1 / (d + 0.3) - 3)) * (1+1j)  x_list = np.linspace(0,5,num=5000) k1 = 1.8 k2 = k1 - 2 * pi  u1_list = np.array([u1(x) for x in x_list]) u1_re_list = u1_list.real u1_im_list = u1_list.imag  u2_list = u1_list * np.exp(2 * pi * 1j * x_list) u2_re_list = u2_list.real u2_im_list = u2_list.imag  exp1_list = np.exp(1j * k1 * x_list) exp1_re_list = exp1_list.real exp1_im_list = exp1_list.imag  exp2_list = np.exp(1j * k2 * x_list) exp2_re_list = exp2_list.real exp2_im_list = exp2_list.imag  psi1_list = u1_list * exp1_list psi1_re_list = psi1_list.real psi1_im_list = psi1_list.imag  psi2_list = u2_list * exp2_list psi2_re_list = psi2_list.real psi2_im_list = psi2_list.imag  assert max(abs(psi1_list - psi2_list)) < 1e-10  fig, ((ax1, ax2), (ax3, ax4), (ax5, ax6)) = plt.subplots(3, 2, sharex=True,                                                          figsize=(6,5)) ax1.set_title('$u_1(x)$') ax1.plot(x_list, u1_re_list, 'b', x_list, u1_im_list, 'r', linewidth=2) ax2.set_title('$u_2(x)$') ax2.plot(x_list, u2_re_list, 'b', x_list, u2_im_list, 'r', linewidth=2) ax3.set_title('$e^{i k_1 x}$') ax3.plot(x_list, exp1_re_list, 'b', x_list, exp1_im_list, 'r', linewidth=2) ax4.set_title('$e^{i k_2 x}$') ax4.plot(x_list, exp2_re_list, 'b', x_list, exp2_im_list, 'r', linewidth=2) ax5.set_title('$\psi(x) = u_1(x) e^{i k_1 x}$') ax5.plot(x_list, psi1_re_list, 'b', x_list, psi1_im_list, 'r', linewidth=2) ax6.set_title('$\psi(x) = u_2(x) e^{i k_2 x}$') ax6.plot(x_list, psi2_re_list, 'b', x_list, psi2_im_list, 'r', linewidth=2) for ax in [ax1, ax2, ax3, ax4, ax5, ax6]:     ax.xaxis.grid(which='major', linestyle='-')     ax.xaxis.set_ticklabels([])     ax.yaxis.set_visible(False)     ax.axhline(y=0, color='k') for ax in [ax1, ax2]:     ax.set_ylim(-3, 3) fig.subplots_adjust(left=0.05, right=0.95, bottom=0.02, top=0.94, hspace=0.3) fig.savefig('/home/steve/Desktop/out.svg') 

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