A projector embedding approach for multiscale coupled-cluster calculations applied to citrate synthase.

Projector-based embedding has recently emerged as a robust and accurate method for the calculation of various electronic molecular properties. We present the coupling of projector embedding with quantum mechanical / molecular mechanical (QM/MM) modeling and apply it for the first time to an enzyme-catalyzed reaction. Using projector-based embedding, we combine coupled-cluster theory, density-functional theory (DFT) and molecular mechanics to compute energies for the proton abstraction from acetyl-coenzyme A by citrate synthase. By embedding correlated ab initio methods in DFT we eliminate functional sensitivity and obtain high-accuracy profiles in a procedure that is straightforward to apply.