Heats of formation of platonic hydrocarbon cages by means of high‐level thermochemical procedures

Abstract

Hydrocarbon cages are key reference materials for the validation and parameterization of computationally cost-effective procedures such as density functional theory (DFT), semiempirical molecular orbital theory, and molecular mechanics. We obtain accurate total atomization energies (TAEs) and heats of formation (Δf H°298) for platonic and prismatic hydrocarbon cages by means of the Wn-F12 explicitly correlated thermochemical protocols. We consider the following kinetically stable (CH)n polycyclic hydrocarbon cages: (i) platonic hydrocarbons (tetrahedrane, cubane, and dodecahedrane), (ii) prismatic hydrocarbons (triprismane, cubane, and pentaprismane), and (iii) one truncated tetrahedrane (octahedrane). Our best theoretical heat of formation for cubane (144.8 kcal mol(-1)) suggests that the experimental value adopted by the NIST thermochemical database (142.7 ± 1.2 kcal mol(-1)) should be revised upwards by ∼2 kcal mol(-1). Our best heat of formation for dodecahedrane (20.2 kcal mol(-1)) suggests that the semiexperimental value (22.4 ± 1 kcal mol(-1)) should be revised downward by ∼2 kcal mol(-1). We use our benchmark Wn-F12 TAEs to evaluate the performance of a variety of computationally less demanding composite thermochemical procedures. These include the Gaussian-n (Gn) and the complete basis set (CBS) methods. The CBS-QB3 and CBS-APNO procedures show relatively poor performance with root-mean-squared deviations (RMSDs) of 4.2 and 2.5 kcal mol(-1), respectively. The best performers of the Gn procedures are G4 and G3(MP2)B3 (RMSD = 0.5 and 0.6 kcal mol(-1), respectively), while the worst performers are G3 and G4(MP2)-6X (RMSD = 2.1 and 2.9 kcal mol(-1), respectively). Isodesmic and even homodesmotic reactions involving these species are surprisingly challenging targets for DFT computations.

W4‐17: A diverse and high‐confidence dataset of atomization energies for benchmarking high‐level electronic structure methods

“…[60] Thus, W1-F12 has been applied to large hydrocarbons (e.g., sumanene, [100] corannulene, [102] and even dodecahedrane) [4] as well as to systems of biological relevance (e.g., guanine [60] and arginine). [60] Thus, W1-F12 has been applied to large hydrocarbons (e.g., sumanene, [100] corannulene, [102] and even dodecahedrane) [4] as well as to systems of biological relevance (e.g., guanine [60] and arginine).…”

“…For example, whereas W1-type methods have been applied to systems with $20 non-hydrogen atoms (vide supra), the largest systems W2-type methods have been applied to include up to $10 non-hydrogen atoms (e.g., cubane [4] and adenine). This, of course, comes with a significant increase in the computational cost.…”

“…[1][2][3][4][5][6][7][8][9][10][11] For example, the performance should improve along the sequence: atomization ! In particular, the accuracy of any given approximate method should increase as larger molecular fragments are conserved on the two sides of the reaction, due to an increasing degree of error cancellation between reactants and products.…”

“…In particular, the accuracy of any given approximate method should increase as larger molecular fragments are conserved on the two sides of the reaction, due to an increasing degree of error cancellation between reactants and products. [1][2][3][4][5][6][7][8][9][10][11] For example, the performance should improve along the sequence: atomization ! isogyric !…”

Thirty years of density functional theory in computational chemistry: an overview and extensive assessment of 200 density functionals

“…However, 24 of the interactions involve platonic hydrocarbon cages [149] and are difficult cases for most density functionals. For the 234 multi-reference systems, however, local functionals and hybrids with a small fraction of exact exchange tend to perform best.…”