Projection-based quantum embedding for periodic systems

Quantum embedding methods are ideal for describing surface chemistry of large periodic systems by using a higher level of theory—such as wave function (WF) theory—for the smaller active site, while still accounting for the quantum mechanical interactions with the electrons in the surrounding environment with a more computationally tractable level of theory such as density functional theory (DFT). We have developed a projection-based quantum embedding approach for the embedding of periodic systems that is numerically exact compared to Kohn-Sham DFT. Furthermore, we show that our method can accurately and efficiently reproduce adsorption and reaction energies from canonical WF methods and experiments.

With Huzinaga projection-based embedding, we have shown that the exact KS-DFT calculations and accurate WF-in-DFT energies can be reproduced if both systems are described using the basis set of the full system. However, we find that improved accuracy and efficiency can be obtained for WF-in-DFT if the subsystems are only described in basis functions associated with that subsystem. This allows for periodic embedding where the smaller active site is described using non-periodic basis functions, and the large environment is treated using periodic basis functions. We have found this approach to be highly accurate and significantly cheaper due to the use of a much reduced basis set for the WF region, and it is broadly applicable to a large number of chemical systems. With this method, we will be able to accurately describe chemistry at interfaces.