2D LHO calculate ground state energy

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Discussion Overview

The discussion revolves around calculating the ground state energy of a two-dimensional harmonic oscillator (2D LHO) given a specific Hamiltonian. Participants explore the implications of various terms in the Hamiltonian and seek to clarify the contributions of different components, particularly focusing on the term involving the product of the coordinates.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a Hamiltonian for a 2D LHO and questions the origin of the term \( \frac{3}{4}(x+y)^2 \).
  • Another participant suggests introducing new variables for the sum and difference of \( x \) and \( y \) to potentially simplify the problem.
  • Several participants express the need for more detailed work to be shown rather than just descriptions of the Hamiltonian's components.
  • There is a discussion about the invariance of the kinetic term under orthogonal transformations and whether this can help in reformulating the potential term.
  • A participant calculates the expectation value of the term containing \( xy \) and finds a discrepancy in dimensional consistency, raising concerns about the validity of their calculations.
  • Another participant points out that the expectation values of \( x \) and \( y \) are correlated and that the expectation value of \( xy \) does not necessarily have to be zero, indicating a misunderstanding in the previous calculations.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the Hamiltonian's terms and the calculation of expectation values. There is no consensus on the resolution of the discrepancies noted in the calculations, and multiple competing perspectives on the approach to the problem remain.

Contextual Notes

Limitations include unresolved mathematical steps regarding the transformation of the potential term and the assumptions made about the expectation values of the wave functions involved.

Das apashanka
A question I have faced in exam to calculate ground state energy
Given Hamiltonian
1/2m(px2+py2)+1/4mw2(5x^2+5y^2+6xy)
ground state energy has to be obtained
Its clear that the Hamiltonian is a 2D LHO Hamiltonian but what for the term 3/4(x+y)2
 
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Where does the last term come from?

It can be interesting to introduce mew variables for the sum and difference of x and y.
 
mfb said:
Where does the last term come from?

It can be interesting to introduce mew variables for the sum and difference of x and y.
I have broken the terms and got hamiltonian of a 2D LHO plus that term
 
It would help if you could show the work instead of describing it like that.
 
mfb said:
It would help if you could show the work instead of describing it like that.
H=1/2m(px2+py2)+mw2/2(x2+y2)+3/4(x2+y2+2xy)
where first two terms are of 2D LHO ,and there is the last term
The ground state energy is to be calculated
 
The kinetic term is invariant under an orthogonal transform of the variables x and y. Can you use this to bring the potential term to a more standard form?
 
DrDu said:
The kinetic term is invariant under an orthogonal transform of the variables x and y. Can you use this to bring the potential term to a more standard form?
Mr Dr Du will you please give some kind of hints to solve this problem
 
For the term containing xy if I directly calculate the expectation value using the ground state wave function the answer is coming as 3mw2/8 which actually dimensionally doesn't match
Since <Φ0(x)Φ0(y)I3mw2xy/2IΦ0(x)Φ0(y)>
expectation value of x and y is 1/2​

Is there any discrepancy regarding this
 
Last edited by a moderator:
Das apashanka said:
Mr Dr Du will you please give some kind of hints to solve this problem
The post was a hint. My first post said basically the same, just a bit more direct. Did you try that?
Das apashanka said:
For the term containing xy if I directly calculate the expectation value using the ground state wave function
You didn't find the ground state wave function yet.
Das apashanka said:
expectation value of x and y is 1/2
The function is symmetric with respect of x and y, the expectation value for both is zero. They are correlated, the expectation value of xy doesn't have to be zero. But you are not yet at the step where you can calculate these things.
 

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