Webinar 60 by Diptarka Hait: Orbital Optimized Density Functional Theory for Electronic Excited States

Time: Thur, Jan 27th, 2022 10:00 AM - 11:00 AM PDT
Watch here: Webinar 60: Orbital Optimized Density Functional Theory for Electronic Excited States | Q-Chem


Density Functional Theory (DFT) based modeling of electronic excited states is of importance for the investigation of the photophysical/photochemical properties and spectroscopic characterization of large systems. The widely-used linear response Time-Dependent DFT (TDDFT) approach is, however, not effective at modeling many types of excited states, including (but not limited to) charge-transfer states, doubly excited states and core-level excitations.
In this webinar, I will discuss the use of state-specific Orbital Optimized (OO) DFT approaches as an alternative to TDDFT for electronic excited states. I will first discuss the motivation and theory behind such approaches, along with some challenges faced by such methods both historically and at present. Subsequently, I will present the Square Gradient Minimization (SGM) algorithm for reliable and efficient excited state orbital optimization, which has been implemented in Q-Chem. In particular, SGM permits use of Restricted Open-shell Kohn-Sham (ROKS) for modeling arbitrary singlet excited states. ROKS/SGM can thus be used to compute core-excitation energies, with the modern SCAN functional yielding ~ 0.3 eV error vs experiment (compared to ~0.1 eV uncertainty in the experimental values themselves). The use of ROKS/SGM in computing Near-Edge X-ray Absorption Fine Structure (NEXAFS) will be discussed. Time permitting, I would also touch upon the recent implementation of the X2C relativistic model in Q-Chem, which (among other things) can be used to accurately compute NEXAFS of elements as heavy as Cr.