Question about how the nabla interacts with wave functions

In summary, the conversation discusses the truth of the statement ψ*∇^2 ψ = ∇ψ*⋅∇ψ and concludes that it is not generally true. However, if the function vanishes on the boundary and partial integration is used, the statement can hold true with a negative sign. The derivative is also mentioned as an anti-hermitian operator.
  • #1
DuckAmuck
236
40
Is the following true?
ψ*∇^2 ψ = ∇ψ*⋅∇ψ

It seems like it should be since you can change the direction of operators.
 
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  • #2
DuckAmuck said:
Is the following true?
ψ*∇^2 ψ = ∇ψ*⋅∇ψ

It seems like it should be since you can change the direction of operators.
No. It is definitely not generally true.

If you have a volume integral and the function vanishes on the boundary, then you can do partial integration to find
$$
\int_V \psi^* \nabla^2 \psi\, dV = - \int_V (\nabla\psi^*)\cdot(\nabla\psi)dV.
$$
Note the minus sign!
 
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  • #3
DuckAmuck said:
It seems like it should be since you can change the direction of operators.
You can do that for hermitian operators. But the derivative is not a hermitian operator. It is an anti-hermitian operator, due to the minus sign explained in the previous post.
 

1. What is the nabla operator and how does it interact with wave functions?

The nabla operator, denoted as ∇, is a mathematical operator used in vector calculus to represent the gradient, divergence, and curl of a vector field. In the context of wave functions, the nabla operator is used to describe the spatial variation of the wave function.

2. How is the nabla operator applied to a wave function?

The nabla operator is applied to a wave function by taking the partial derivatives of the wave function with respect to each spatial coordinate. This results in a vector quantity known as the gradient of the wave function.

3. What is the significance of the nabla operator in quantum mechanics?

In quantum mechanics, the nabla operator is used to describe the spatial behavior of particles and their associated wave functions. It is a fundamental tool in understanding the behavior of quantum systems and is used in many important equations, such as the Schrödinger equation.

4. How does the nabla operator affect the shape of a wave function?

The nabla operator affects the shape of a wave function by describing the rate of change of the wave function in different directions. This can result in changes to the amplitude and phase of the wave function, ultimately affecting its overall shape.

5. Can the nabla operator be applied to all types of wave functions?

Yes, the nabla operator can be applied to all types of wave functions, including scalar, vector, and tensor wave functions. However, the specific form of the operator and its effects on the wave function may differ depending on the type of wave function being considered.

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