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

Ryan D Reynolds; Takeshi Yanai; Toru Shiozaki

doi:10.1063/1.5036594

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

J Chem Phys. 2018 Jul 7;149(1):014106. doi: 10.1063/1.5036594.

Authors

Ryan D Reynolds¹, Takeshi Yanai², Toru Shiozaki¹

Affiliations

¹ Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208, USA.
² Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya 464-8602, Japan.

PMID: 29981535
DOI: 10.1063/1.5036594

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.