State-of-the-Art Quantum Chemistry Meets Variable Reaction Coordinate Transition State Theory to Solve the Puzzling Case of the H₂S + Cl System

Abstract

The atmospheric reaction of H 2 S with Cl has been re-investigated in order to check if, as previously suggested, only explicit dynamical computations can lead to an accurate evaluation of the reaction rate because of strong recrossing effects and the breakdown of the variational extension of transition state theory. For this reason, the corresponding potential energy surface has been thoroughly investigated, thus leading to an accurate characterization of all stationary points, whose energetics has been computed at the state of the art. To this end, coupled-cluster theory including up to quadruple excitations has been employed, together with the extrapolation to the complete basis set limit and also incorporating core-valence correlation, spin-orbit, and scalar relativistic effects as well as diagonal Born-Oppenheimer corrections. This highly accurate 1

The Role of State-of-the-Art Quantum-Chemical Calculations in Astrochemistry: Formation Route and Spectroscopy of Ethanimine as a Paradigmatic Case

“…Incorporation of the fT and pQ contributions provides negligible effects, the only exceptions being TS2, TS3 and TS4, for which deviations of about 2– 3 mol −1 are noted. As expected from our previous experience [ 24 , 33 , 61 ], the results obtained by using the ChS model are accurate. In fact, they are within mol −1 from the corresponding CBS+CV values, and within 2 mol −1 with respect to CBS+CV+fT+pQ results.…”

“…Our strategy relies on this model when larger systems are involved. In the present context, it has been employed to further demonstrate its high accuracy and reliability, which was already pointed out in References [ 24 , 33 , 61 ].…”

“…Since the double-hybrid B2PLYP functional [ 55 ] represents a good compromise between accuracy and computational cost for both structural and spectroscopic properties [ 56 , 57 , 58 ] and is able to provide a reliable description of reactive and non-reactive PESs [ 34 , 35 , 56 , 57 , 59 , 60 , 61 , 62 ], our strategy relies on it in order to provide the final description of the stationary points from a structural point of view. For this purpose, B2PLYP is usually employed in conjunction with a triple-zeta basis sets incorporating diffuse functions.…”

Toward Accurate Formation Routes of Complex Organic Molecules in the Interstellar Medium: The Paradigmatic Cases of Acrylonitrile and Cyanomethanimine

“…To reduce the computational cost of these two latter contributions, they are evaluated using Møller-Plesset perturbation theory to the second order [MP2; (Møller and Plesset, 1934)]. Within any 'cheap' scheme, as well tested in the literature (Lupi et al, 2020b;Alessandrini et al, 2021;Lupi et al, 2021), the MP2 energy is extrapolated using the n −3 formula proposed by Helgaker and coworkers (Helgaker et al, 1997). Overall, the jun-Cheap energy is given by the following expression:…”

“…To benchmark the performance of the two model chemistries introduced above, reference electronic energies are obtained by means of the so-called HEAT-like (HL) scheme, closely resembling the original HEAT methodology proposed by Stanton and co-workers (Tajti et al, 2004;Bomble et al, 2006;Harding et al, 2008;Lupi et al, 2020b), and entirely based on the CC ansatz. In this benchmark, the HL composite scheme is built on top of geometries optimized at the jun-Cheap level:…”