Finding Value of Phi*k(x) in Basis Function Method

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    Basis Function Method
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Discussion Overview

The discussion revolves around the determination of the value of Phi*k(x) in the context of the basis function method, particularly focusing on the orthonormality of basis functions used in quantum mechanics or similar fields. Participants explore the implications of orthonormality and conditions necessary for a set of functions to be considered orthonormal.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant states that to find Cn in the equation Psi(x) = Σ CnΦn(x), one must multiply both sides by Φ*k(x) and integrate, resulting in Ck when n = k.
  • Another participant questions whether the basis set {Φn} is orthonormal and suggests multiplying the equation by Φ*k*(x), summing over k, and integrating over x.
  • A participant asks for the conditions under which the set {Φn} is orthonormal.
  • Another participant provides a definition of orthonormality, stating that the inner product ⟨Φi|Φj⟩ must equal δij for the set to be orthonormal.
  • One participant requests an example of an orthonormal set of functions.
  • A later reply lists examples of orthonormal functions, including hydrogenoid functions, simple harmonic oscillator (SHO) eigenfunctions, and functions from the infinite square well problem.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the specific value of Phi*k(x) and the conditions for orthonormality. While some definitions and examples are provided, no consensus is reached on the exact nature of Phi*k(x) or the conditions for orthonormality.

Contextual Notes

Participants reference the need for orthonormality in the context of quantum mechanics without fully resolving the mathematical steps or assumptions involved in determining Phi*k(x).

Who May Find This Useful

This discussion may be of interest to students and professionals in physics and mathematics, particularly those studying quantum mechanics and functional analysis.

ohhhnooo
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Psi(x) = Sumationn CnPhin(x)

in order to find Cn, i have to multiply both side of the above equation by Phi*k(x) and take the integral. The result is Ck if n = k. My question is what is the value of Phi*k(x)?

i know that multiplying both side of the equation by Phi*k(x) would make the function orthonormal when n != k, and normalize when n = k. But i don't know how to find it.
 
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Is this:[tex]\psi(x)=\sum_{n}C_{n}\phi_{n}(x)[/tex](1)...?

Is the basis [tex]\{\phi_{n} \}_{n=1}^{\infty}[/tex] orthonormal...?If so,then multiply (1) by [itex]\phi_{k}^{*}(x)[/itex],sum after "k" & integrate after "x"...

Daniel.
 
what is the condition for [tex]\{\phi_{n} \}_{n=1}^{\infty}[/tex] to be orthonormal? thanks
 
ohhhnooo said:
what is the condition for [tex]\{\phi_{n} \}_{n=1}^{\infty}[/tex] to be orthonormal? thanks
Per definition, if the following holds, the set [itex]\{\phi_{n} \}_{n=1}^{\infty}[/itex] is orthonormal:

[tex]\langle \phi_i|\phi_j\rangle = \int \limits_{-\infty}^{+\infty}\phi_i^*(x)\phi_j(x)\; dx=\delta_{ij}[/tex]
 
can you provide an example?
 
Hidrogenoid functions are an interesting example.SHO eigenfunctions are other example.Rigid rotator is another example.Infinite square well and so on,and so forth.

Daniel.
 

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