Journal
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Volume 14, Issue 2, Pages 588-596Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.7b00832
Keywords
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Funding
- U.S. Department of Energy [DE-SC0006863]
- NSF Office of Advanced Cyberinfrastructure [OAC-1663636, CHE-1565520]
- Student Technology Fee
- National Science Foundation [MRI-1624430]
- Direct For Mathematical & Physical Scien [1565520] Funding Source: National Science Foundation
- Division Of Chemistry [1624430] Funding Source: National Science Foundation
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Projected Hartree-Fock (PHF) theory can restore important symmetries to broken symmetry wave functions. Variation after projection (VAP) implementations make it possible to deliberately break and then restore a given symmetry by directly minimizing the projected energy expression. This technique can be applied to any symmetry that can be broken from relaxing constraints on single Slater determinant wave functions. For instance, generalized Hartree-Fock (GHF) wave functions are eigenfunctions of neither (S) over cap (z) nor S-2. By relaxing these constraints, the wave function can explore a larger variational space and can reach lower energies than more constrained HF solutions. We have implemented spin-projected GHF (SGHF), which retains many of the advantages of breaking symmetry while also being a spin eigenfunction, with some notable improvements over previous implementations. Our new algorithm involves the formation of new intermediate matrices not previously discussed in the literature. Discretization of the necessary integration over the rotation group SO(3) is also accomplished much more efficiently using Lebedev grids. A novel scheme to incrementally build rotated Fock matrices is also introduced and compared with more standard approaches.
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