An introduction to coupled-cluster theory, and recent developments in quantum embedding

In this talk I will give a pedagogical introduction to how coupled-cluster theory works, from the perspectives of both the coupled-cluster wavefunction and the underlying diagrammatic many-body theory. One challenge for the application of coupled-cluster theory in chemistry is its computational expense. I will describe efforts in our group and elsewhere to use multiscale embedding theories to capture the benefits of coupled-cluster accuracy at greatly reduced computational cost; in particular I will show that combinations of coupled-cluster and density functional theory provide an attractive framework for accurate modelling of chemical reactivity.