The complete-active-space self-consistent-field (CASSCF) method is able to recover large amounts of static correlation. Due to its exponential scaling, however, conventional implementations are limited to relatively small active spaces of about 18 electrons in 18 orbitals. Previous strategies to reduce the cost of CASSCF, such as quantum monte carlo and heat-bath configuration interaction, still result in exponential scaling. Applying the many-body expansion—also known as the method of increments—to CASSCF (iCASSCF) has been shown to produce a polynomially scaling method that both retains the accuracy of the parent theory and is capable of treating full-valence active spaces. The Fock matrix is a key quantity in electronic structure theory used in orbital optimization and gradient calculation. Prior implementations for building the Fock matrix in iCASSCF rely on symmetrization to remove variations in active-active orbital rotations. Herein, a new scheme to stabilize the orbital optimization and obtain precise analytical geometric gradients is presented. We demonstrate the ability of this method to recover full-valence correlation in large systems, such as an Mn(salen) complex with 84 electrons in 84 orbitals, that would be prohibitively expensive using conventional CASSCF.<br/>

Variational procedure for the many-body expansion of the CASSCF energy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.