- #1
jarvinen
- 13
- 0
I need to calculate [itex] \left[ H , \ \frac{1}{r} \mathbf{r} \right] [/itex].
My initial idea is to use [itex] \left[ H, \ U \mathbf{r} \right] = \left[ H, \ U \right] \mathbf{r} + U \left[ H , \ \mathbf{r} \right] [/itex].
Then clearly [itex] \left[H , \ U \right] \psi = \frac{ - \hbar ^{2} }{2m} \left( \nabla ^{2} \left( U \psi \right) - U \nabla ^{2} \psi \right) = 0 [/itex] in this case (as U = 1/r).
So we only have [itex] \left[ H, \ \mathbf{r} \right] [/itex] to consider.
I am only interested in the first component so I do [itex] \left[ H, \ r \right] = \frac{- \hbar ^{2}}{2m} \frac{2}{r} [/itex].
Is this correct? I ask because it seems out-of-place in the rest of the question (which I can add later if the above is right).
My initial idea is to use [itex] \left[ H, \ U \mathbf{r} \right] = \left[ H, \ U \right] \mathbf{r} + U \left[ H , \ \mathbf{r} \right] [/itex].
Then clearly [itex] \left[H , \ U \right] \psi = \frac{ - \hbar ^{2} }{2m} \left( \nabla ^{2} \left( U \psi \right) - U \nabla ^{2} \psi \right) = 0 [/itex] in this case (as U = 1/r).
So we only have [itex] \left[ H, \ \mathbf{r} \right] [/itex] to consider.
I am only interested in the first component so I do [itex] \left[ H, \ r \right] = \frac{- \hbar ^{2}}{2m} \frac{2}{r} [/itex].
Is this correct? I ask because it seems out-of-place in the rest of the question (which I can add later if the above is right).