Chapter 12: Harmonic Oscillators and Other Spatially-varying Wells

In this chapter we will consider eigenstates of potential energy functions that are spatially varying, V(x) ≠ constant. We begin with the most recognizable of these problems, that of the simple harmonic oscillator, V(x) = mω2x2/2, is perhaps the most ubiquitous potential energy function in physics. Several systems in nature exactly exhibit the harmonic oscillator's potential energy, but many more systems approximately exhibit the form of the harmonic oscillator's potential energy.1

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1A generic potential energy function, V(x), can be expanded in a Taylor series to yield

V(x) = V(x0) + (xx0) dV(x)/dx|x = x0 + ((xx0)2/2!) d2V(x)/dx2|x = x0+…

If the original potential energy is symmetric about x = 0, we can expand about x0 = 0 to yield

V(x) = V(x0) + (x) dV(x)/dx|x = 0 + (x2/2!) d2V(x)/dx2|x = 0 + …

The leading non-constant term is in the form of a harmonic oscillator, and thus this potential can be approximately treated as a harmonic oscillator.

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