Ab initioand DFT studies on van der Waals trimers: The OCS · (CO₂)₂complexes

Abstract

Ab initio calculations [MP2, MP4SDTQ, and QCISD(T)] using different basis sets [6-31G(d,p), cc-pVXZ (X = D, T, Q), and aug-cc-pVDZ] and density functional theory [B3LYP/6-31G(d,p)] calculations were carried out to study the OCS.(CO2)2 van der Waals trimer. The DFT has proved inappropriate to the study of this type of systems where the dispersion forces are expected to play a relevant role. Three minima isomers (two noncyclic and one cyclic) were located and characterized. The most stable isomer exhibits a noncyclic barrel-like structure whose bond lengths, angles, rotational constants, and dipole moment agree quite well with the corresponding experimental values of the only structure observed in recent microwave spectroscopic studies. The energetic proximity of the three isomers, with stabilization energies of 1442, 1371, and 1307 cm-1, respectively, at the CBS-MP2/cc-pVXZ (X = D, T, Q) level, strongly suggests that the two unobserved structures should also be detected as in the case of the (CO2)3 trimer where both noncyclic and cyclic isomers have been reported to exist. The many-body symmetry-adapted perturbation theory is employed to analyze the nature of the interactions leading to the formation of the different structures. The three-body contributions are small and stabilizing for the two most stable structures and almost negligible for the cyclic isomer.

Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

“…It is interesting to observe that the CPR correction changes the activation energy in the correct direction but it is too big, probably as a consequence of the overcorrection associated with the CP algorithm to correct for BSSE at the correlated level. 33 As concluded in recent studies 34,35 where the CP values are compared with those arising from the application of BSSE-free methods, the real values must lie somewhere between the NCP and CPR estimates.…”

“…A number of authors 33 noticed overcorrections when the CP method is applied at the correlated levels. Further, recent works 34,35 where BSSE-free techniques, like the symmetryadapted perturbation theory (SAPT) 36 or complete basis set (CBS) 37 extrapolations, are employed seem to provide arguments confirming that apparent limitation of the CP method. However, in any case, experience suggests that the CP correction is useful to provide upper limits for the interaction energies.…”

Theoretical insights on electron donor–acceptor interactions involving carbon dioxide

“…The physical meaningful components of the interaction energy were obtained using symmetry-adapted perturbation theory (SAPT), which has already been successfully used to study some intermolecular complexes of carbon dioxide. [30][31][32] The role of basis set superposition errors (BSSE) on interaction energies and geometries was estimated using the counterpoise correction method [33] and the seven-point scheme of Dannenberg and coworkers. [34,35] …”

Computational investigation of the CH3XC=S...S (X = H, HO, HS, PH2, CH3) bonding type

“…At the same time, interaction potentials ΔE 2 at the MP2/ cc-pVTZ level of theory are also presented in Table 2. It is obvious that the BSSE is overestimated by the counterpoise method [23][24][25][26]. However, the MP2/ cc-pVTZ level of theory is free of BSSE and computationally feasible for the complexes studied here.…”