Free Particle 1D: Box Normalization Question

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In a one-dimensional free particle scenario with zero potential, the boundary condition \(\psi(x+L) = e^{i\theta}\psi(x)\) introduces an arbitrary phase \(\theta\). The discussion highlights that while the energy expression \(E = k^2\hbar/(2m)\) remains valid, the presence of \(\theta\) raises questions about its impact on energy levels. It is suggested that the phase should not be disregarded when applying boundary conditions, as it may have implications in contexts like Bloch waves in crystal lattices. The normalized eigenfunctions can be expressed as \(\psi_n(x) = L^{-1/2} \exp(i(2\pi n/L)x + i\theta)\), but clarity on the necessity of \(\theta\) in energy calculations is sought. Understanding the physical significance of the boundary condition is crucial for accurate solutions.
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Free particle in 1D where V(x) = 0. There is a general boundary condition \psi(x+L)=e^{i\theta}\psi(x) used for box normalization which has arbitrary phase theta. E=k^2\hbar/(2m) is true for free particle energies.

Attempt

Comparing with the condition \psi(x+L)=\psi(x) I don't see how I will get different energies E since L is still the maximum wavelength, therefore \lambda = L/n = 2\pi/k or k = 2n\pi/L for n = 1, 2, ...; and then energies E_n can be computed.

How do I get theta dependence into the energies for the case \psi(x+L)=e^{i\theta}\psi(x)? Or maybe the better question is do I need theta dependence in the energies for a correct solution? Shouldn't the phase of a wave function have no physical significance?

Given the k above is true then my normalized eigenfunctions would be \psi_n(x) = L^{-1/2} \exp(i(2\pi n/L)x+i\theta)? ...But I'm not sure that k is correct.

Can anyone clear this up for me? Much thanks.
 
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The phase is arbitrary, but that does not mean that you can set it to zero when applying the boundary condition.

It may help to consider the physical meaning of the boundary condition above, which occurs when you have translational symmetry in crystal lattices (Bloch waves).

http://www.iue.tuwien.ac.at/phd/smirnov/node41.html
 

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