4 center integrals

[joshkamm]

For Vaibhav use cases, we need these to be reasonably parallel and we need a good grid.

It's probably not that difficult to code but it will be tedious

• Alex and Vaibhav talk about the theory of the theory of the integrals
• After some thinking, come back and talk to Paul about their thoughts

The 4 center integrals are a major bottleneck because they need a larger grid size and there are the most of them. If we can reduce the grid size requirement that would make a major performance impact on the code. If not, we will want to focus more on parallelization to improve the performance.