IMPROVEMENTS TO LOCAL CONFIGURATION INTERACTION METHODS

Abstract

TigerCI is a program implementing methods for local multireference singles and doubles configuration interaction and is used to study molecules with complex electronic structures. The current implementation of TigerCI as a plug-in to MOLCAS, a proprietary quantum chemistry package, presents challenges for flexibility, maintainability, and code sharing. A new “stand-alone” version of TigerCI is presented which removes all dependencies on MOLCAS and replaces them using Erkale and libint, which are open-source libraries. Stand-alone TigerCI maintains all functionality available with the original plug-in version, while offering similar accuracy and performance. The orbital localization and two-electron integral decomposition routines were re-written and optimized. Furthermore, additional and improved functionality is added to stand-alone TigerCI beyond what was available in the plug-in version, including the expansion of the behavior of spheres and cylinders used in the local approximation in TigerCI. Stand-alone TigerCI then was used for the calculation of oxidation potentials for a dinitroxide biradical species currently under investigation for potential anti-microbial properties.