We here develop a fully quantum embedded version of initiator full configuration interaction quantum Monte Carlo (i-FCIQMC) and apply it to study an ionic bond (lithium hydride, LiH) and a covalent bond (hydrogen flouride, HF) physisorbed to a benzene molecule. The embedding is performed using a recently developed Huzinaga projection operator approach, which affords good synergy with i-FCIQMC by minimizing the number of orbitals in the calculation. When considering the dissociation energy of these bonds into closed-shell ionic fragments, we find that i-FCIQMC embedded in density functional theory (i-FCIQMC-in-DFT) delivers comparable accuracy with coupled cluster singles and doubles with perturbative triples embedded in density functional theory (CCSD(T)-in-DFT). In treating the bond dissociation energy curve of HF, i-FCIQMC-in-DFT has improved accuracy over CCSD(T)-in-DFT due to the presence of strong correlation. We discuss the implications of the new i-FCIQMC-in-DFT method as applied to bond breaking in catalysis.
Bibliographical noteFunding Information:
This research is supported by the Nanoporous Materials Genome Center, funded by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award DE-FG02-17ER16362. J.J.S. and H.R.P. acknowledge the University of Iowa for funding.
D.S.G. and J.D.G. acknowledge an award of computer time was provided by the ASCR Leadership Computing Challenge (ALCC) program. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231. D.S.G. and J.D.G. acknowledge additional computer resources were provided by the Minnesota Supercomputing Institute (MSI) at the University of Minnesota. J.J.S. and H.R.P. acknowledge the University of Iowa Informatics Initiative (UI3) for computer resources. The code used throughout this work was HANDE ( hande.org.uk ), QSoME ( github.com/Goodpaster/QSoME ), and PySCF ( sunqm.github.io/pyscf/ ).