You can simulate a lot of atoms with a modern supercomputer. The only problem is just how many atoms there are even in a tiny grain of sand. However that doesn’

You can simulate a lot of atoms with a modern supercomputer. The only problem is just how many atoms there are even in a tiny grain of sand. However that doesn’t mean all hope is lost. You just have to get really clever - there is a lot of repeating patterns in a grain of sand - you don’t really need to simulate all or even most of it. The same holds true for most structures.