PNNL

Abstract

We report the development of a novel diagnostic tool, named WFOT (wavefunction overlap tool), designed to evaluate the overlap between wavefunctions computed at single reference (i.e. TDDFT or CIS) and multi-reference (i.e. CASSCF/CASPT2) electronic structure levels of theory. It relies on truncating of the single- and multi-reference WFs to CIS-like expansions spanning the same configurational space and maximizing the molecular orbital overlap by means of a unitary transformation. To demonstrate the functionality of the tool, we calculate the transient spectrum of acetylacetone by evaluating excited state absorption signals with multi-reference quality on top of single-reference on-the-fly dynamics simulations. Semi-automatic spectra generation is facilitated by interfacing the tool with the COBRAMM package, which also allows one to use WFOT with several quantum chemistry codes such as Gaussian, NWChem, and OpenMolcas. Other exciting possibilities for the utilization of the code beyond the simulation of transient absorption spectroscopy are eventually discussed.