◎代POST
◎急需




( A)(1)for the delta-function potential with P<<1,
       find at k=0 the energy of the lowest energy band
    (2) for the same problem find the band gap at k= π/a


( B)(3) show that for diamond stucture the Fourier component
        Ug of the crystal potential seen by an electron is
        equal to zero for G=2A

(4) show that in the usual first-order approximation to the
    solutions of the wave equation in a periodic lattice the
    energy gap vanishes at the zone boundary plane normal to
    the end of the vector A



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