Avoided crossing

Imagine you have two toys - a ball and a car. These two toys want to play together, but they have to be careful not to bump into each other.

Now, if you hold the ball and the car close to each other, you'll notice something interesting happening - the ball and the car don't want to be in the same place at the same time!

This is kind of like how electrons in atoms and molecules behave. Electrons are tiny particles that move around atoms or molecules. Sometimes, when two electrons get close to each other, they don't want to be in the same place, just like our ball and car.

This is called an avoided crossing. It's like the electrons are playing a game of "tag" - they're trying to chase each other, but they can't both be in the same spot at the same time.

Now, when electrons avoid each other like this, it can affect the properties of the material they're in. This is why scientists study avoided crossings – because they help us understand how materials behave at the atomic and molecular level, and this can help us make new materials or improve existing ones.