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# Tag Info

## Hot answers tagged quantum-mechanics

### Non-hermitian discretizations in quantum mechanics

If your discrete equations represent your problem properly you should have the right eigenvalues, although numerically you can get a small imaginary part when solving the eigenvalue problem. As an ...
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### Calculating partial trace of array in NumPy

I didn't follow exactly your notation so I can't say for sure what this would look like for your example, but two suggestions: if you really want your life made simple, check out ...
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### Solving the time dependent Schrödinger equation with leapfrog integration in 1D

I read through the paper you linked and they give the stability condition for this method to be (eq. A6) $$\frac{-2}{\Delta t} \le V \le \frac{2}{\Delta t} - \frac{2}{m \Delta r^2}$$ This has to be ...
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### Calculating partial trace of array in NumPy

I don't have enough reputation to comment, but I wanted to give a basic complement of gIS's answer. Simply put, if we have the decomposition over $V=V_1\otimes V_2$, which we represent with, say, the ...
• 61
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### Normalizing a density matrix at each iteration

As always with numerical problems, it's a good idea to simplify things as much as possible to isolate what's really going wrong. You can simplify the problem by considering the evolution of a pure ...
• 10.3k
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### Numerical solution to the infinite well problem

I think that the main problem might be with the solver you are using. The Hamiltonian (matrix) in this case is Hermitian, it is even symmetric since it is purely real. You could use ...
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### Zero Eigenvalues in Lanczos Algorithm

The SciPy tutorial explicitly states Note that ARPACK is generally better at finding extremal eigenvalues: that is, eigenvalues with large magnitudes. In particular, using ...
• 12.3k
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### Discrepancies between numerical and analytical solution for particle in a finite potential well?

I think that your potential for the numerical case is wrong. The potential should be a big positive number, so the solution tends to zero outside the well when the value of the potential increases. ...
• 8,525
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### Numerical solution of zero-potential time-dependent Schrödinger equation in 1D

Regarding the boundary conditions: Don't be fooled by Wikipedia. Yes, the scenario in the picture suggests an absorption at the boundaries, and yes, one could use absorbing boundary conditions in ...
• 3,147
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### How can I evaluate more accurate energy eigenvalues from Schrodinger equation using shooting method?

Your problem was the lower limit of integration. It should have been $-x_e$ instead of 0, since $x_e$ is the equilibrium point for the potential and not the minimum distance. After correcting that, ...
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### Problems with the time-dependent Schrödinger equation solutions

First, you're solving the Schrödinger equation not in a box, but rather you apply periodic boundary conditions. That is, it's more like solving the TDSE on a ring. But this just as a comment and ...
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### Computing eigenvalues of Schrodinger equation with spin

When modelling spin in the Schrödinger equation, one has several alternatives which need to be chosen in advance. I'll copy an excerpt from a work of mine to give an overview (it considers atomic ...
• 3,147
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### What will be the impact of quantum computing on existing numerical techniques (e.g. CFD)?

There are two major reasons that there is no tag quantum-computing (at least yet) in Computational Science SE: There is a specialized Quantum Computing StackExchange community. I am not aware of ...
• 8,672
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### Recommendation for a fixed-step ODE solver?

I think DifferentialEquations.jl in Julia has a very comprehensive suite of ODE solvers, including the ones you mentioned (Adams-Bashfort and GBS) and many others. This Julia library is becoming more ...
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