Since the 1980s, I would say that the biggest advances are the new accurate DFT functionals, the widespread use of the resolution-of-the-identity and other rank-reduction techniques, as well as the implementation of linear-scaling methods. Other new aspects include local correlation schemes and the widespread use of first-principles molecular dynamics. Also, the quantum mechanics/molecular mechanics approach has been very useful to study biological systems.

In other areas, new methods based on the understanding of entanglement, like the matrix product states work that came from renormalization group theory and now from quantum information efforts are very promising.

So for looking at Shillady’s book, I think one needs to go beyond the chapter titles for more detail.

Having said all this, I consider the electronic structure theory field a “mature” field, in comparison to the other field I am working on right now: quantum information where I feel a faster pace of discovery by the community.

What am I missing? What would you say is the biggest change in electronic structure theory in the last 15 to 20 years?