Congratulations to our PhD student Ivan Giannì and our Postdoctoral researcher Tommaso Nottoli for their publication entitled "MBE-CASSCF Approach for the Accurate Treatment of Large Active Spaces" in the Journal of Chemical Theory and Computation. The work presents a novel implementation of the complete active space self-consistent field (CASSCF) method that makes use of the many-body expanded full configuration interaction (MBE-FCI) method to incrementally approximate electronic structures within large active spaces.
On the basis of a hybrid first-order algorithm employing both Super-CI and quasi-Newton strategies for the optimization of molecular orbitals, we demonstrate both computational efficacy and high accuracy of the resulting MBE-CASSCF method. We assess the performance of our implementation on a set of established numerical tests before applying MBE-CASSCF in the investigation of the triplet-quintet spin gap of iron(II) porphyrin with active spaces as large as 50 electrons in 50 orbitals.
The work is available at https://pubs.acs.org/doi/10.1021/acs.jctc.4c00388
