<SYSTEM_TASK:>
Given the following text description, write Python code to implement the functionality described below step by step
<END_TASK>
<USER_TASK:>
Description:
 Tight Binding program to compute the band structure of simple semiconductors.
Parameters taken from Vogl, Hjalmarson and Dow,
A Semiempirical Tight-Binding Theory of the Electronic Structure
of Semiconductors, 
J. Phys. Chem. Sol. 44 (5), pp 365-378 (1983).
Step1:  Interpolated SiGe band structure
The band structure for Si(1-x)Ge(x) is supposedly well approximated by a linear interpolation of the Si and Ge band structures.
Step2:  Plotting misc parts of Brillouin zones
Compare Si and Ge CBs.
<ASSISTANT_TASK:>
Python Code:
%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
from numpy.linalg import eigvalsh
from collections import namedtuple
import TB
TB.band(TB.Si)
TB.band(TB.GaAs)
TB.band(TB.Ge)
Explanation: Tight Binding program to compute the band structure of simple semiconductors.
Parameters taken from Vogl, Hjalmarson and Dow,
A Semiempirical Tight-Binding Theory of the Electronic Structure
of Semiconductors, 
J. Phys. Chem. Sol. 44 (5), pp 365-378 (1983).
End of explanation
def SiGe_band(x=0.2):
    Si_data = TB.bandpts(TB.Si)
    Ge_data = TB.bandpts(TB.Ge)
    data = (1-x)*Si_data + x*Ge_data
    TB.bandplt("SiGe, %%Ge=%.2f" % x,data)
    return
SiGe_band(0)
SiGe_band(0.1)
SiGe_band(0.25)
SiGe_band(0.37)
Explanation: Interpolated SiGe band structure
The band structure for Si(1-x)Ge(x) is supposedly well approximated by a linear interpolation of the Si and Ge band structures.
End of explanation
Ge_CB = TB.bandpts(TB.Ge)[:,4]
Si_CB = TB.bandpts(TB.Si)[:,4]
nk = len(Si_CB)
n = (nk-2)//3
plt.plot(Si_CB)
plt.plot(Ge_CB)
TB.band_labels(n)
plt.axis(xmax=3*n+1)
plt.plot(Si_CB,label='Si')
plt.plot(Ge_CB,label='Ge')
plt.plot(0.9*Si_CB + 0.1*Ge_CB,label='Si_0.9 Ge_0.1')
TB.band_labels(n)
plt.axis(xmax=3*n+1)
plt.legend(bbox_to_anchor=(1.05, 1), loc=2, borderaxespad=0.)
min_Si = min(Si_CB)
min_Ge = min(Ge_CB)
print min_Si, min_Ge
# min_Si - min_Ge = 0.12
Si_CB_shifted = Si_CB - min_Si + min_Ge + 0.12
Explanation: Plotting misc parts of Brillouin zones
Compare Si and Ge CBs.
End of explanation
<END_TASK>