The Kohn-Sham DFT formalism with approximate exchange correlation (XC) functionals suffer from several prominent classes of errors for both the ground and excited states. I will discuss our recent efforts to address these complementary challenges. In the ground state, transition metal complexes are notoriously difficult to study accurately with approximate DFT. Few systematic studies have been done for the quantification and elimination of density delocalization error (DDE). We focus on curation of accurate reference densities for transition metal compounds in order to identify the degree and impact of DDE on energetic properties. We use accurate multireference wavefunction based methods to generate near exact reference densities for a broad range of transition metal compounds in various spin and oxidation states with equilibrium and distorted structures. We then quantify the DDE of some commonly used XC functionals on these systems and compare the effect of some common EDE elimination techniques, including DFT+U, global/range-separated hybrid tuning, and constrained DFT on influencing DDE. In the excited state, LR-TDDFT is incapable of correctly describing the topography of potential energy surfaces at conical intersections, an essential component of studying non-adiabatic dynamics. The state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS) method is a computationally efficient alternative that retains the attractive scaling features of its KS-DFT parent. The application of SI-SA-REKS to photochemistry was previously hampered by the lack of analytical nuclear gradients and non-adiabatic coupling matrix elements. We have recently derived analytical energy derivatives for SI-SA-REKS and implemented the method on graphical processing units (GPUs) for improved computational efficiency. We demonstrate that our implementation affords mean-field computational cost while enabling an accurate description of conical intersections.

Understanding and correcting DFT errors in ground and excited electronic states

256th National Meeting (2018)

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