Ab Initio and Density Functional Theory Reinvestigation of Gas-Phase Sulfuric Acid Monohydrate and Ammonium Hydrogen Sulfate

Abstract

We have calculated the thermochemical parameters for the reactions H 2 SO 4 + H 2 O T H 2 SO 4 ‚H 2 O and H 2 -SO 4 + NH 3 T H 2 SO 4 ‚NH 3 using the B3LYP and PW91 functionals, MP2 perturbation theory and four different basis sets. Different methods and basis sets yield very different results with respect to, for example, the reaction free energies. A large part, but not all, of these differences are caused by basis set superposition error (BSSE), which is on the order of 1-3 kcal mol -1 for most method/basis set combinations used in previous studies. Complete basis set extrapolation (CBS) calculations using the cc-pV(X+d)Z and aug-ccpV(X+d)Z basis sets (with X ) D, T, Q) at the B3LYP level indicate that if BSSE errors of less than 0.2 kcal mol -1 are desired in uncorrected calculations, basis sets of at least aug-cc-pV(T+d)Z quality should be used. The use of additional augmented basis functions is also shown to be important, as the BSSE error is significant for the nonaugmented basis sets even at the quadruple-level. The effect of anharmonic corrections to the zero-point energies and thermal contributions to the free energy are shown to be around 0.4 kcal mol -1 for the H 2 SO 4 ‚H 2 O cluster at 298 K. Single-point CCSD(T) calculations for the H 2 SO 4 ‚H 2 O cluster also indicate that B3LYP and MP2 calculations reproduce the CCSD(T) energies well, whereas the PW91 results are significantly overbinding. However, basis-set limit extrapolations at the CCSD(T) level indicate that the B3LYP binding energies are too low by ca. 1-2 kcal/mol. This probably explains the difference of about 2 kcal mol -1 for the free energy of the H 2 SO 4 + H 2 O T H 2 SO 4 ‚H 2 O reaction between the counterpoise-corrected B3LYP calculations with large basis sets and the diffusion-based experimental values of S. M. Ball, D. R. Hanson, F. L Eisele and P. H. McMurry (J. Phys. Chem. A. 2000, 104, 1715. Topological analysis of the electronic charge density based on the quantum theory of atoms in molecules (QTAIM) shows that different method/basis set combinations lead to qualitatively different bonding patterns for the H 2 SO 4 ‚NH 3 cluster. Using QTAIM analysis, we have also defined a proton transfer degree parameter which may be useful in further studies.

Amines in the Earth’s Atmosphere: A Density Functional Theory Study of the Thermochemistry of Pre-Nucleation Clusters

“…The most stable isomers (within 2 kcal mole í1 of the most stable isomer/global minimum) obtained at the PW91PW91/6-31+G* level have been optimized using the PW91PW91/6-311+G(3df,3pd) method to obtain the final results. The choice of the computational method is based on the satisfactory performance of the PW91PW91 [46] on atmospheric clusters, including predicting the Gibbs free energies, structural characteristics and vibrational spectra in a very good agreement with experiments and ab initio studies, and availability of large amount of data for different atmospheric species/clusters computed at PW91PW91/6-311+G(3df,3pd) level of theory for comparison [24][25][26][27][28][29][30]34]. The availability of data for ternary sulfuric acid-water-ammonia clusters computed at the same level of theory is a very important factor because the assessment of different nucleation pathways, which is based on the analysis of the reaction free energies computed using the same method, is clearly more legitimate than that based on the comparison of results obtained at different levels of theory [47].…”

“…The ability of computational quantum chemical methods to provide an adequate description of molecular interactions in nucleating vapours has been pointed out in Nadykto et al [24], in which the classical problem of the ion sign preference established in back 1897 by Wilson [1] has been solved. Recently, computational chemical studies of atmospheric species have become a focus of intense activity [24][25][26][27][28][29][30][31][32][33][34][35][36]. Although a large number of the computational quantum studies considering atmospheric clusters has been published within the last five years, only a few are dedicated to the interaction of common organics with atmospheric nucleation precursors [32,34,35].…”

Computational Study of the Clustering of a Cyclohexene Autoxidation Product C6H8O7 with Itself and Sulfuric Acid

“…Along the trajectory several cluster structures were extracted, the geometry was optimized, and frequencies were calculated. The lowest identified molecular structure of the ( 5 cluster is shown in Figure 5 calculated using the M06-2X functional.…”

Investigating Atmospheric Sulfuric Acid–Water–Ammonia Particle Formation Using Quantum Chemistry

“…An error analysis study by Kurtén et al [66] found that the B3LYP density functional underestimates the binding energy of sulfuric acid-water and sulfuric acid-ammonia clusters compared to high-level coupled-cluster methods. The underestimation of B3LYP binding energies for sulfuric acid-water was also noted by Al Natsheh et al [55] and Nadykto and Yu [67].…”

“…Even computational methods with relatively large systematic errors can thus yield useful and reliable data, as long as the errors are constant for the set of systems compared. For example, a test comparison [66] of 12 computational methods (3 theories and 4 basis sets, with and without counterpoise corrections) yielded differences as large as 5 kcal/mol for the absolute value of the binding energy of the H 2 SO 4 ·NH 3 cluster, but all predicted values within about 2 kcal/mol from each other for the difference in binding energies of the H 2 SO 4 ·NH 3 and H 2 SO 4 ·H 2 O clusters. The latter value, as discussed in [38] and [68] is much more important for assessing the role of ammonia in sulfuric acidwater nucleation.…”