Effects of the Level of Electronic Structure Theory on the Dynamics of the F^– + CH₃I Reaction

Abstract

Accuracy of the different levels of electronic structure theory is frequently studied for stationary-point properties; however, little is known about the effects of the electronic structure methods and basis sets on the dynamics of chemical reactions. Here we report such an investigation for the F + CHI S2 and proton-transfer reactions by developing 20 different analytical potential energy surfaces (PESs) obtained at the HF/DZ, HF/TZ, HF-D3(BJ)/DZ, HF-D3(BJ)/TZ, MP2/DZ, MP2/TZ, MP2-F12/DZ, MP2-F12/TZ, CCSD/DZ, CCSD-F12b/DZ, CCSD(T)/DZ, CCSD(T)-F12b/DZ, OQVCCD(T)/DZ, B97-1/TZ, PBE0/TZ, PBE0-D3(BJ)/TZ, M06-2X/TZ, M06-2X-D3(0)/TZ, B2PLYP/TZ, and B2PLYP-D3(BJ)/TZ levels of theory, where DZ and TZ denote the aug-cc-pVDZ and aug-cc-pVTZ basis sets with a relativistic effective core potential and the corresponding bases for iodine. Millions of quasiclassical trajectories on these PESs reveal that (a) in the case of standard methods, increasing the basis from DZ to TZ decreases the S2 cross sections by 20-30%; (b) the explicitly correlated F12 reactivity is converged with a DZ basis;

First-Principles Reaction Dynamics beyond Six-Atom Systems

“…If the perturbative (T) approximation breaks down, a Brueckner-type coupled-cluster-based composite method could be useful as shown for OH – + CH 3 I . Furthermore, quasi-variational coupled-cluster methods were developed recently, which also showed promising behavior in our dynamics studies. , Finally, we emphasize that several first-principles reaction dynamics studies proved that theory is capable of providing results in excellent agreement with experiment. We hope that new experiments will also be carried out for post-six-atom reactions, thereby moving the field forward hand in hand with theory.…”

Advances and New Challenges to Bimolecular Reaction Dynamics Theory

“…Most current PESs ,,, are based on high-level ab initio electronic structure theories, such as coupled cluster singles, doubles, and perturbative triples (CCSD­(T)) and multireference configuration interaction (MRCI) methods, which account for electron correlation, and their F12 variants . Interestingly, some density functional theory-based PESs reported recently have shown promise to rival high-level theories at significantly less computational costs, , but their general applicability still needs further confirmation. Unlike nonreactive systems, reactions involve bond breaking and forming, which are often accompanied by significant changes in the electronic structure.…”

Bridging the Gap between Direct Dynamics and Globally Accurate Reactive Potential Energy Surfaces Using Neural Networks

“…One notes that the detailed reaction dynamics may be dependent on the electronic structure theory employed. 55,56 In general, once the DFT-based PES is obtained, it can be easily improved by replacing the DFT energies and atomic forces with those obtained from high-level wave function-based methods, if they are computationally affordable. Combined with the sophisticated quasi-quantization binning scheme for polyatomic molecules, this strategy can be especially useful for stimulating polyatomic reactions at the state-to-state level.…”

“…Without any special treatment, our novel strategy is certainly not limited to the current system and is expected to simplify and boost the development of reactive PESs for very complex systems, although the minimum number of BOMD trajectories to develop high-dimensional PESs certainly depends on the initial conditions of trajectories, the data collection scheme, and the complexity of the system. One notes that the detailed reaction dynamics may be dependent on the electronic structure theory employed. , In general, once the DFT-based PES is obtained, it can be easily improved by replacing the DFT energies and atomic forces with those obtained from high-level wave function-based methods, if they are computationally affordable. Combined with the sophisticated quasi-quantization binning scheme for polyatomic molecules, this strategy can be especially useful for stimulating polyatomic reactions at the state-to-state level.…”