C–H⋯O H-bonded complexes: How does basis set superposition error change their potential-energy surfaces?

Abstract

Geometries, vibrational frequencies, and interaction energies of the CNH¯O 3 and HCCH¯O 3 complexes are calculated in a counterpoise-corrected ͑CP-corrected͒ potential-energy surface ͑PES͒ that corrects for the basis set superposition error ͑BSSE͒. Ab initio calculations are performed at the Hartree-Fock ͑HF͒ and second-order Mo "ller-Plesset ͑MP2͒ levels, using the 6-31G(d,p) and D95ϩϩ(d, p) basis sets. Interaction energies are presented including corrections for zero-point vibrational energy ͑ZPVE͒ and thermal correction to enthalpy at 298 K. The CP-corrected and conventional PES are compared; the uncorrected PES obtained using the larger basis set including diffuse functions exhibits a double well shape, whereas use of the 6-31G(d,p) basis set leads to a flat single-well profile. The CP-corrected PES has always a multiple-well shape. In particular, it is shown that the CP-corrected PES using the smaller basis set is qualitatively analogous to that obtained with the larger basis sets, so the CP method becomes useful to correctly describe large systems, where the use of small basis sets may be necessary.

MH⋅sHX Dihydrogen Bond with M≡Li, Na and X≡F, Cl, Br: A CP-Corrected PES Calculation and an AIM Analysis

“…Because the complex uses a basis set larger than the one used by monomers, in most cases this error models the complex to be too attractive. As it has been studied before, when BSSE is corrected along the whole surface, important changes in the potential energy surface appear, not only in the energy but also in the position of the minimum as well as its topology [19,20]. In this article the counterpoise correction (CP) proposed by Boys and Bernardi [21] is used to correct the potential energy surface's BSSE, geometry and frequencies.…”

The hardness profile as a tool to detect spurious stationary points in the potential energy surface

“…To this end, we have chosen a series of well-known chemical processes for which the use of a too much rigid basis set or a too simple method of calculation leads to wrong PESs. [33][34][35][36][37][38][39] The results obtained will reveal that the hardness profile can be used as a good indicator of the presence of spurious stationary points on the calculated PES.…”

“…At the HF and MP2 levels, the equilibrium geometry of HCCH¯O 3 has C 2v symmetry with the 6-31G(d,p) basis set, whereas with the D95ϩϩG basis set it has a lower C s symmetry. Salvador et al 39 evidenced some years later that the spurious C 2v equilibrium geometry obtained with the 6-31G(d,p) basis set was due to the BSSE. Thus, these authors found that when the BSSE is corrected during the geometry optimization process, both the 6-31G(d,p) and D95ϩϩG basis sets predict the same C s equilibrium geometry.…”

“…It has been found for a number of systems that the location of minima and transition states in the PES is exposed to dramatic changes depending on the methodology and basis set used. [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] This is particularly true in the case of reactions involving weak inter and/or intramolecular interactions. In these reactions, the number and/or the nature of stationary points ͑minima or transition states͒ may change with the basis set and/or the method of calculation ͓for instance, by including or not the basis set superposition error ͑BSSE͒ in the calculation of the PES ͑Refs.…”

“…Thus, these authors found that when the BSSE is corrected during the geometry optimization process, both the 6-31G(d,p) and D95ϩϩG basis sets predict the same C s equilibrium geometry. 39 Figure 7 depicts the E and 1 profiles for the linear transit path defined by the angle between a line perpendicular to the C 2 axis of the ozone molecule and the line that connects the H with the central oxygen of the O 3 molecule ͑the ЄHOX angle in Fig. 1͒ computed at the B3LYP level using the 6-31G, 6-31G(d,p), 6-311ϩϩG(d,p), and aug-ccpVDZ basis sets.…”