Full-dimensional potential energy surface for acetylacetone and tunneling splittings

Abstract

New, full-dimensional potential energy surface for acetylacetone allows for description of H-tunneling dynamics and characterization of stationary points.

Breaking the Coupled Cluster Barrier for Machine-Learned Potentials of Large Molecules: The Case of 15-Atom Acetylacetone

“…The best estimate of this barrier height is 1148 cm –1 (3.29 kcal/mol), based on CCSD(T)-F12/aug-cc-pVTZ single-point calculations at the LCCSD(T)-optimized geometries. Therefore, the Δ-ML PES slightly overestimates the barrier height; nevertheless, it is a significant improvement over the MP2-based PES, 13 which has a barrier height of 745 cm –1 (2.13 kcal/mol).…”

“… 9 Indeed this has been verified for N -methylacetamide, 9 , 10 tropolone, 12 and AcAc. 13 Note that these PESs use the most recent software that includes gradients in the fit and produces gradients on output. 25 − 27…”

“…The histogram of the MP2 database from our AcAc PES 13 is shown in Figure 1 (a); it includes 5454 geometries. The MP2 energies are relative to the MP2 global minimum.…”

“… 32 It was used in our work on AcAc based on the MP2 PES ( V LL ). 13 Briefly, a 1d potential, denoted V ( Q im ), which is the minimum-energy path as a function of the imaginary-frequency mode ( Q im ) of the H-transfer saddle point, was obtained by optimizing all of the other coordinates at fixed Q im values using the V LL → CC PES except for the methyl rotors, which cannot be described using rectilinear normal coordinates. These are held fixed at the saddle point values all the way along the path.…”

“…Because of the fixed methyl orientation and fitting error, the barrier height of this 1d Q im path is 1055 cm –1 and it is 179 cm –1 lower than the LCCSD(T) value. Therefore, we “morphed” this 1d potential using the same strategy as described previously 13 so that it gives the correct barrier height (1234 cm –1 ). The two mass-scaled 1d potentials employed (one for H and the other for D transfer) are shown in Figure 4 .…”