A hierarchical family of three-dimensional potential energy surfaces for He-CO

Abstract

A hierarchical family of five three-dimensional potential energy surfaces has been developed for the benchmark He-CO system. Four surfaces were obtained at the coupled cluster singles and doubles level of theory with a perturbational estimate of triple excitations, CCSD͑T͒, and range in quality from the doubly augmented double-zeta basis set to the complete basis set ͑CBS͒ limit. The fifth corresponds to an approximate CCSDT/CBS surface ͑CCSD with iterative triples/CBS, denoted CBS+ corr͒. The CBS limit results were obtained by pointwise basis set extrapolations of the individual counterpoise-corrected interaction energies. For each surface, over 1000 interaction energies were accurately interpolated using a reproducing kernel Hilbert space approach with an R −6 + R −7 asymptotic form. In each case, both three-dimensional and effective two-dimensional surfaces were developed. In standard Jacobi coordinates, the final CBS+ corr surface has a global minimum at r CO = 2.1322a 0 , R = 6.418a 0 , and ␥ = 70.84°with a well depth of −22.34 cm −1 . The other four surfaces have well depths ranging from −14.83 cm −1 ͓CCSD͑T͒/d-aug-cc-pVDZ͔ to −22.02 cm −1 ͓CCSD͑T͒/CBS͔. For each of these surfaces the infrared spectrum has been accurately calculated and compared to experiment, as well as to previous theoretical and empirical surfaces. The final CBS+ corr surface exhibits root-mean-square and maximum errors compared to experiment ͑ 4 He͒ of just 0.03 and 0.04 cm −1 , respectively, for all 42 transitions and is the most accurate ab initio surface to date for this system. Other quantities investigated include the interaction second virial coefficient, the integral cross sections, and thermal rate coefficients for rotational relaxation of CO by He, and rate coefficients for CO vibrational relaxation by He. All the observable quantities showed a smooth convergence with respect to the quality of the underlying interaction surface.

Quantum dynamical resonances in low-energy CO(j = 0) + He inelastic collisions

“…As stressed in the introduction, an accurate PES is an essential ingredient of the scattering calculations. Five three-dimensional PESs were published in 2005 for CO-He, four of which were obtained at the CCSD(T) level with different basis sets 26 . The fifth PES, which should be the most accurate, is an approximate CCSD(T)/CBS surface.…”

“…2) 24,25 . These experiments, as well as the quantum scattering close-coupling calculations performed on two different PESs calculated (1) at the singles and doubles coupled cluster level with perturbative triples and extrapolation to the complete basis set (CCSD(T)/CBS) 26 and (2) with symmetry-adapted perturbation theory (SAPT) 27 are described in the Methods.…”

Basis set convergence of potential energy surfaces: Ground electronic state of H2 and H

“…Some of this extrapolation schemes have been used in the estimation of the CBS energies for PES calculations63–67, nevertheless, there are not convergence studies that analyze the most appropriate expression for PES calculations. In this study, as mentioned earlier, we examine the convergence behavior of total energies of the ground electronic PES of H 2 and H with the family of correlation consistent basis sets.…”

Observation of quantum dynamical resonances in near cold inelastic collisions of astrophysical molecules

“…7 compares our experimental ICSs for CO ( j = 0) + He → CO ( j = 1) + He in the threshold region with theoretical ones obtained by close-coupling calculations performed with two different PESs 29. The two PESs had been previously calculated (i) with symmetry-adapted perturbation theory (SAPT) and (ii) at the singles and doubles coupled cluster level with perturbative triples and extrapolation to the complete basis set (CCSD(T)/CBS) 40,41. It can be seen in panel (a) that the ICSs obtained with the two PESs are very similar and that the experimental data are in very good agreement with the theoretical ICSs curves convoluted over the collision energy spread.…”