Determination of time-dependent coefficients (QM)

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SUMMARY

The discussion centers on the determination of time-dependent coefficients, C_n(t), in the context of quantum mechanics, specifically for a benzene system. The equation under consideration is Ψ(r,t) = ∑ C_n(t) e^{-i E_n t} ψ(r). The user initially struggled with the transition from time-independent to time-dependent coefficients, leading to erroneous electron density calculations. The resolution involved correcting the equation to ψ(r,t) = ∑ C_n(t) exp(-iE_n t) ψ_n(r) and ensuring the orthonormalization of vectors.

PREREQUISITES
  • Understanding of quantum mechanics principles, particularly wave functions.
  • Familiarity with Hückel's method for molecular orbital theory.
  • Knowledge of orthonormality in vector spaces.
  • Basic proficiency in mathematical notation used in quantum equations.
NEXT STEPS
  • Study the application of Hückel's method in greater detail.
  • Learn about orthonormalization techniques in quantum mechanics.
  • Explore the implications of time-dependent Schrödinger equations.
  • Investigate numerical methods for solving quantum mechanical equations.
USEFUL FOR

Students and researchers in quantum mechanics, particularly those focusing on molecular systems and time-dependent phenomena, will benefit from this discussion.

Aeon
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Hi,

I am trying to solve the following equation:

\Psi(r,t) = \sum_n C_n(t) e^{-i E_n t} \psi(r)

to find the C_n(t)s.

The system I am modeling is benzene. I can, by Hückel's method, determine the time-independent solution. The apparently obvious transition from time-independent coefficients to time-dependent coefficients is troubling me. A simple plot of the squared coefficients indicates that my electron density vanishes, which is indicative of error.

I'm wondering how is the proper way to solve for the time-dependent coefficients...
 
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Did you leave off a subscript? If you meant to write ψ(r,t) = ∑ Cn(t) exp(-iEnt) ψn(r) where the ψn(r)'s are orthonormal, then
∫ψ(r,t) ψn(r) dr = Cn(t) exp(-iEnt), which gives you Cn.
 
I forgot a subscript, you are right.

Also, the problem was that my vectors were not orthogonalized. Thanks!
 

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