Jennifer R. DeRosa

The ability of Large Language Models (LLMs) to outperform humans on many intellectual tasks has created a difficult landscape for assessing student work. One strategy is designing assignments to be specifically difficult for AI. However, LLMs have been shown to perform well on general chemistry problems across topics, and new models continue to make AI-proofing assignments more difficult. In this work, we evaluate the recently released GPT-5 Thinking model across a set of 1736 questions from the Openstax general chemistry textbook. While GPT-5 achieves near-perfect accuracy overall, categorizing questions by the types of cognitive skills required elucidates specific weaknesses. Notably, GPT-5 tends to make major errors when asked to create figures. These findings inform best practices for AI-resistant assignment design.

We investigate the applicability of the Condon approximation (i.e., the notion that the diabatic coupling is invariant to geometry) in the context of both electron transfer (ET) and triplet energy transfer (TET) and compare the two cases. Although it is well appreciated that diabatic couplings usually arise from the interactions of electronic wave function tails, we show that ET tails are very different from TET tails. Using a simple model problem, our analysis explains in detail why the rates of TET decays with twice the rate of ET, while also leading to the hypothesis that the smaller diabatic couplings found for TET (versus ET) should imply more sensitivity to non-Condon fluctuations. As an example, for the classic sets of molecules investigated by Closs, we show that the Condon approximation is indeed less applicable for TET than for ET.

Marcus theory is the workhorse of theoretical chemistry for predicting the rates of charge and energy transfer. Marcus theory overwhelmingly agrees with experiment─both in terms of electron transfer and triplet energy transfer─for the famous set of naphthalene-bridge-biphenyl and naphthalene-bridge-benzophenone systems studied by Piotrowiak, Miller, and Closs. That being said, the agreement is not perfect, and in this manuscript, we revisit one key point of disagreement: the molecule C-13-ae ([3,equatorial]-naphthalene-cyclohexane-[1,axial]-benzophenone). To better understand the theory-experiment disagreement, we introduce and employ a novel scheme to sample the seam between two diabatic electronic states (E-SHAKE) through which we reveal the breakdown of the Condon approximation and the presence of a conical intersection for the C-13-ae molecule; we also predict an isotopic effect on the rate of triplet-triplet energy transfer.

We revisit the naked transition metal cation (Ti⁺) and methanol reaction and go beyond the standard Landau-Zener (LZ) picture when modeling the intersystem crossing (ISC) rate between the lowest doublet and quartet states. We use both (i) unconstrained Born-Oppenheimer molecular dynamics (BOMD) calculations with an approximate two-state method to estimate population transfer between spin diabats and (ii) constrained dynamics to explore energetically accessible portions of the N_DOF - 1 crossing seam, where N_DOF is the total number of internal degrees of freedom. Whereas previous LZ calculations (that necessarily relied on the Condon approximation to be valid) fell short and predicted much slower crossing probabilities than shown in experiment, we show that ISC can occur rapidly because the spin-orbit coupling (SOC) between the doublet and quartet surfaces can vary by 2 orders of magnitude (depending on where in the seam the crossing occurs during dynamics) and the crossing region is revisited multiple times during a dynamics run of a few hundred femtoseconds. We further isolate the two important nuclear coordinates that tune the SOC and modulate the transition, highlighting exactly how and why organometallic ISC can occur rapidly for small systems with floppy internal nuclear vibrational modes.