Recent News

One of the challenges in simulating photochemical reactions is that there are essentially no electronic structure methods that are accurate, efficient, and robust enough to be applied to a wide variety of systems. Enter Resonating Hartree-Fock (ResHF), which is a promising solution to this conundrum because it provides balanced accuracy for different types of excited states, and has mean-field scaling. However, the original ResHF method is not numerically stable. In a new paper, Ericka solves this problem by reformulating the ResHF equations in terms of the matrix adjugate. With this approach, ResHF becomes fully numerically stable, and can thus be applied to a wider variety of systems than has been possible previously.

This paper was published in the Journal of Chemical Physics, “Numerically Stable Resonating Hartree-Fock”.

John’s paper introducing the “rid” preconditioner for TDDFT is now available online in The Journal of Chemical Physics. This paper is the culmination of two intertwined threads in John’s research: 1) the use of semiempirical preconditioners to accelerate the convergence of ab initio TDDFT calculations; and 2) the development of the TDDFT-ris model for fast and accurate simulations of spectra. Using the rid preconditioner, TDDFT excitation energies are converged in about 5 iterations on average, which is about a factor of 3 faster than using the conventional (diagonal) preconditioner. Even more, this speedup is obtained without any loss of accuracy. The full paper is titled “Converging TDDFT calculations in 5 iterations with minimal auxiliary preconditioning”.

The group’s contribution to the cyclobutanone prediction challenge is now published online in The Journal of Chemical Physics. This paper was a true group effort, with Ericka and Sean leading the way. For this prediction challenge, groups were tasked with predicting the photochemical dynamics of cyclobutanone after being excited by 200 nm light. What made this challenge especially exciting is that all of these contributions will be stress tested by comparing to ultrafast electron diffraction experiments that were performed concurrently with the simulations. In effect, it was a double-blind experiment to definitively answer the question: “Just how predictive are our simulations, really?” The full paper is titled “Ultrafast Photochemistry and Electron Diffraction for Cyclobutanone in the S₂ State: Surface Hopping with Time-Dependent Density Functional Theory”.

John Zhou’s paper introducing the TDDFT-ris model was recently published in The Journal of Physical Chemistry Letters. In this paper, we introduce a minimal auxiliary basis set approach to approximate TDDFT using a resolution-of-the-identity approximation with just a single s-function per atom. TDDFT-ris reproduces TDDFT excited states with a mean error of about 0.06 eV while reducing the cost by a factor of 200-300. The full paper is titled “Minimal Auxiliary Basis Set Approach for the Electronic Excitation Spectra of Organic Molecules”.