The Variational Localized Active Space Self-Consistent Field Method

Abstract

Fragmentation methods applied to multireference wave functions constitute a road towards the application of highly accurate ab initio wave function calculations to large molecules and solids. However, it is important for reproducibility and transferability that a fragmentation scheme be well-defined with minimal dependence on initial orbital guesses or user-designed ad hoc fragmentation schemes. One way to improve this sort of robustness is to ensure the energy obeys a variational principle; i.e., that the active orbitals and active space wave functions minimize the electronic energy in a certain ansatz for the molecular wave function. We extended the theory of the localized active space self-consistent field, LASSCF, method (JCTC 2019, 15, 972) to fully minimize the energy with respect to all orbital rotations, rendering it truly variational. The new method, called vLASSCF, substantially improves the robustness and reproducibility of the LAS wave function compared to LASSCF. We analyze the storage and operation cost scaling of vLASSCF compared to orbital optimization using a standard CASSCF approach and we show results of vLASSCF calculations on some simple test systems. We show that vLASSCF is energetically equivalent to CASSCF in the limit of one active subspace, and that vLASSCF significantly improves upon the reliability of LASSCF energy differences, allowing for more meaningful and subtle analysis of potential energy curves of dissociating molecules. We also show that all forms of LASSCF have a lower operation cost scaling than the orbital-optimization part of CASSCF.

References in corpus (13)

• Density matrix embedding: A simple alternative to dynamical mean-field theory
• Density matrix embedding: A strong-coupling quantum embedding theory
• Orbital Optimization in the Density Matrix Renormalization Group, with applications to polyenes and β-carotene
• A practical guide to density matrix embedding theory in quantum chemistry
• Automated construction of molecular active spaces from atomic valence orbitals
• Computational characterization and prediction of metal-organic framework properties
• Projected Hartree-Fock Theory
• Entanglement in solvable many-particle models
• Exactly-embedded multiconfigurational self-consistent field theory using density matrix embedding: the localized active space self-consistent field method
• Active space decomposition with multiple sites: Density matrix renormalization group algorithm
• A cluster-based mean-field and perturbative description of strongly correlated fermion systems. Application to the 1D and 2D Hubbard model
• Five years of density matrix embedding theory
• Orbital Optimization in the Active Space Decomposition Model

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