ELI5: Explain Like I'm 5

Variational method (quantum mechanics)

Let's say you have a magic box, and you want to know what's inside it. However, you can't just look inside the box because it's not transparent. Quantum mechanics is like this magic box, and we want to figure out what's going on inside.

One way to approach this problem is to use the variational method. This method is like putting on different pairs of glasses and seeing which one helps you see better inside the box.

In quantum mechanics, we have a special equation called the Schrödinger equation that tells us how everything in the magic box behaves. We want to know the solution to this equation so we can figure out what's inside.

The variational method involves guessing what the solution might be and plugging it into the Schrödinger equation to see how well it fits. We call this guessed solution a trial wave function.

We then use the trial wave function to calculate the energy of the system. If the trial wave function fits the Schrödinger equation well, then the energy calculation will be accurate. If not, then we need to try a different trial wave function and repeat the process.

This method helps us get closer to the true solution because we are using a guess-and-check approach to find the best wave function. Think of it like trying on different pairs of glasses until we find the one that helps us see the inside of the magic box the best.

Overall, the variational method is a helpful tool in solving the Schrödinger equation and figuring out what's going on inside the magic box of quantum mechanics.