Large-scale relativistic complete active space self-consistent field with robust convergence

Abstract

We report an efficient algorithm using density fitting for the relativistic complete active space self-consistent field (CASSCF) method, which is significantly more stable than the algorithm previously reported by one of the authors [J. E. Bates and T. Shiozaki, J. Chem. Phys. 142, 044112 (2015)]. Our algorithm is based on the second-order orbital update scheme with an iterative augmented Hessian procedure, in which the density-fitted orbital Hessian is directly contracted to the trial vectors. Using this scheme, each microiteration is made less time consuming than one Dirac-Hartree-Fock iteration, and macroiterations converge quadratically. In addition, we show that the CASSCF calculations with the Gaunt and full Breit interactions can be efficiently performed by means of approximate orbital Hessians computed with the Dirac-Coulomb Hamiltonian. It is demonstrated that our algorithm can also be applied to systems under an external magnetic field, for which all of the molecular integrals are computed using gauge-including atomic orbitals.

References in corpus (3)

• BAGEL: Brilliantly Advanced General Electronic-structure Library
• A general second order complete active space self-consistent-field solver for large-scale systems
• Second-Order Self-Consistent-Field Density-Matrix Renormalization Group

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• A trust-region augmented Hessian implementation for state-specific and state-averaged CASSCF wave functions
• Insight on Gaussian basis set truncation errors in weak to intermediate magnetic fields with an approximate Hamiltonian
• Numerically Exact Configuration Interaction at Quadrillion-Determinant Scale
• A Reusable Library for Second-Order Orbital Optimization Using the Trust Region Method