Explicit correlation and intermolecular interactions: Investigating carbon dioxide complexes with the CCSD(T)-F12 method

Abstract

We have optimized the lowest energy structures and calculated interaction energies for the CO(2)-Ar, CO(2)-N(2), CO(2)-CO, CO(2)-H(2)O, and CO(2)-NH(3) dimers with the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)]-F12 methods and the associated VXZ-F12 (where X = D,T,Q) basis sets. For a given cardinal number, we find that results obtained with the CCSD(T)-F12 methods are much closer to the CCSD(T) complete basis set limit than the conventional CCSD(T) results. The relatively modest increase in the computational cost between explicit and conventional CCSD(T) is more than compensated for by the impressive accuracy of the CCSD(T)-F12 method. We recommend use of the CCSD(T)-F12 methods in combination with the VXZ-F12 basis sets for the accurate determination of equilibrium geometries and interaction energies of weakly bound electron donor acceptor complexes.

Communication: Spectroscopic observation of the O-bonded T-shaped isomer of the CO-CO2 dimer and two of its intermolecular frequencies

“…6,7 Shortly after the gas phase studies, a number of theoretical ab initio calculations appeared which predicted the existence of two T-shaped isomers, a C-bound (the most stable isomer) and an O-bound (a higher energy structure). [8][9][10][11] As shown below, our new infrared spectra confirm the existence and stability of the T-shaped O-bonded CO 2 -CO in a helium buffer. Additionally, we measure two of the four intermolecular frequencies of this isomer.…”

“…10 However, a more recent and higher level ab initio calculation 11 gives a corrected binding energy of 409 cm −1 for isomer 1. Anyway, it seems clear from theory that isomer 1 (C-bonded) is considerably more strongly bound than isomer 2 (O-bonded).…”

Communication: THz absorption spectrum of the CO2–H2O complex: Observation and assignment of intermolecular van der Waals vibrations

“…Numerous quantum-chemical studies of the systems' intermolecular potential energy surface (IPES) have been reported. [3][4][5][6][7][8][9][10][11][12][13] High level of electron correlation, extensive basis sets, and inclusion of basis set superposition errors prove mandatory as the IPES is extremely flat near the global potential energy minimum. A recent comprehensive work reports a complete 5D ab initio IPES composed of 23 000 high level single-point energies in configuration space and settles that the global potential energy minimum has a planar and T-shaped geometry of C 2v symmetry with the oxygen atom of H 2 O bound to the C atom and the H atoms pointing away from the CO 2 molecule 14 ( Fig.…”

Interpolation of intermolecular potentials using Gaussian processes

“…The C-C distance of 3.23Å from the PES is 0.01Å larger than the minimum distance taken from the best literature calculation 22 ; both are lower than the experimental distance of 3.277Å 21 , mainly as a result of non-rigidity of the intermolecular bond. A direct calculation of the interaction energy for this geometry gives −1.859 × 10 −3 E h , which is within 0.01 × 10 −3 E h of the best calculated value 22 . The difference of ∼ 0.03 × 10 −3 E h between the PES and calculation is similar to the RMSE of 0.024 × 10 −3 E h reported in section III.…”