I am a condensed matter theorist and I mostly use quantum Monte Carlo methods. I use models like the Heisenberg model, an represent an extreme simplification of real materials to just localized spin degrees of freedom (no electrons, orbitals, etc).
The advantage of this extreme simplification is it allows much more precise studies of the underlying physics. The disadvantage is that it can be difficult to make direct connections to experiments.
I know very little about how ab initio methods work and even less about how they treat magnetism. I would like to have a better sense of the capabilities of these methods.
- Is it possible to model strong magnetic correlations or magnetic phase transitions?
- Can ab initio methods be used to calculate exchange parameters (like the Heisenberg $J$)?