Equation cropping up in Kronig Penny model

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In summary, the conversation discusses how to solve an equation for E as a function of K using the equation cos(k*a)=P*sin(u*a)/u*a + cos(u*a), where u=sqrt(2*m*E)/h-bar. It is mentioned that this equation cannot be solved analytically, so an approximation method is suggested. The solution involves plotting the right-hand side of the equation to get a sinusoidal waveform and considering the left-hand side as a continuum of values between +1 and -1. The discussion also mentions band gaps and provides a link for further information.
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quantumfireball
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Homework Statement



how does one solve the following equation to obtain E as a function of K.




Homework Equations



cos(k*a)=P*sin(u*a)/u*a + cos(u*a),
where u=sqrt(2*m*E)/h-bar




The Attempt at a Solution


theres no way this can be solved analytically,however how to go about approximating E as a function of k.
E(k) is obviously a many to one function.
 
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Step1: Plot the RHS of the equation to get a sinusoidal waveform

The LHS is just a continum of values from +1 to -1 since Cos cannot exceed these limits for all values of ka... This means the LHS gives us any number between +1 and -1

Now imagine the graph that you plotted in step 1. Imagine two lines at +1 and -1 cutting off this graph... All points within these 2 lines represent valid energies... all others are "forbidden energies" or band gaps

This link might be useful to you:

http://webphysics.davidson.edu/facul...nig-penney.htm

particularly Fig 8.11 Pg 297
 
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FAQ: Equation cropping up in Kronig Penny model

What is the Kronig Penny model?

The Kronig Penny model is a simplified quantum mechanical model used to describe the behavior of electrons in a one-dimensional periodic potential. It is often used to study the properties of materials with a periodic crystal structure, such as metals and semiconductors.

What is the significance of equation cropping up in the Kronig Penny model?

The equation that arises in the Kronig Penny model is known as the Schrödinger equation, which describes the wave-like behavior of particles at a quantum level. It is significant because it allows us to understand the behavior of electrons in a periodic potential and make predictions about the properties of materials.

How does the equation in the Kronig Penny model relate to the energy levels of electrons?

The equation in the Kronig Penny model, also known as the tight-binding approximation, relates the energy levels of electrons to the periodic potential of the material. It shows that the energy levels are quantized, meaning they can only take on certain discrete values, and the width of the potential well determines the spacing between these levels.

Can the Kronig Penny model be applied to other systems besides materials with a periodic crystal structure?

Yes, the Kronig Penny model can be applied to other systems, such as atoms, molecules, and even some artificial structures. However, it is most commonly used to study the properties of materials with a periodic crystal structure.

How does the Kronig Penny model support our understanding of band theory in materials?

The Kronig Penny model is a simplified version of the more complex band theory, which explains the electronic structure of materials. It provides a clear and intuitive way to understand the behavior of electrons in a periodic potential and how it leads to the formation of energy bands in materials. It also helps us understand how changes in the periodic potential can affect the electronic properties of a material.

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