dorsal/arxiv
View SchemaHeats of formation of perchloric acid, HClO$_4$, and perchloric anhydride, Cl$_2$O$_7$. Probing the limits of W1 and W2 theory
| Authors | Jan M. L. Martin |
|---|---|
| Categories | |
| ArXiv ID | physics/0508076 |
| URL | https://arxiv.org/abs/physics/0508076 |
| DOI | 10.1016/j.theochem.2006.03.035 |
| Journal | J. Mol. Struct. (THEOCHEM) 771, 19-26 (2006) |
Abstract
The heats of formation of HClO$_4$ and Cl$_2$O$_7$ have been determined to chemical accuracy for the first time by means of W1 and W2 theory. These molecules exhibit particularly severe degrees of inner polarization, and as such obtaining a basis-set limit SCF component to the total atomization energy becomes a challenge. (Adding high-exponent $d$ functions to a standard $spd$ basis set has an effect on the order of 100 kcal/mol for Cl$_2$O$_7$.) Wilson's aug-cc-pV(n+d)Z basis sets represent a dramatic improvement over the standard aug-cc-pVnZ basis sets, while the aug-cc-pVnZ+2d1f sequence converges still more rapidly. Jensen's polarization consistent basis sets still require additional high-exponent $d$ functions: for smooth convergence we suggest the \{aug-pc1+3d,aug-pc2+2d,aug-pc3+d,aug-pc4\} sequence. The role of the tight $d$ functions is shown to be an improved description of the Cl (3d) Rydberg orbital, enhancing its ability to receive back-bonding from the oxygen lone pairs. In problematic cases like this (or indeed in general), a single SCF/aug-cc-pV6Z+2d1f calculation may be preferable over empirically motivated extrapolations. Our best estimate heats of formation are $\Delta H^\circ_{f,298}[$HClO$_4$(g)$]=-0.6\pm$1 kcal/mol and $\Delta H^\circ_{f,298}[$Cl$_2$O$_7$(g)$]=65.9\pm$2 kcal/mol, the largest source of uncertainty being our inability to account for post-CCSD(T) correlation effects. While G2 and G3 theory have fairly large errors, G3X theory reproduces both values to within 2 kcal/mol.
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"abstract": "The heats of formation of HClO$_4$ and Cl$_2$O$_7$ have been determined to\nchemical accuracy for the first time by means of W1 and W2 theory. These\nmolecules exhibit particularly severe degrees of inner polarization, and as\nsuch obtaining a basis-set limit SCF component to the total atomization energy\nbecomes a challenge. (Adding high-exponent $d$ functions to a standard $spd$\nbasis set has an effect on the order of 100 kcal/mol for Cl$_2$O$_7$.) Wilson\u0027s\naug-cc-pV(n+d)Z basis sets represent a dramatic improvement over the standard\naug-cc-pVnZ basis sets, while the aug-cc-pVnZ+2d1f sequence converges still\nmore rapidly. Jensen\u0027s polarization consistent basis sets still require\nadditional high-exponent $d$ functions: for smooth convergence we suggest the\n\\{aug-pc1+3d,aug-pc2+2d,aug-pc3+d,aug-pc4\\} sequence. The role of the tight $d$\nfunctions is shown to be an improved description of the Cl (3d) Rydberg\norbital, enhancing its ability to receive back-bonding from the oxygen lone\npairs. In problematic cases like this (or indeed in general), a single\nSCF/aug-cc-pV6Z+2d1f calculation may be preferable over empirically motivated\nextrapolations. Our best estimate heats of formation are $\\Delta\nH^\\circ_{f,298}[$HClO$_4$(g)$]=-0.6\\pm$1 kcal/mol and $\\Delta\nH^\\circ_{f,298}[$Cl$_2$O$_7$(g)$]=65.9\\pm$2 kcal/mol, the largest source of\nuncertainty being our inability to account for post-CCSD(T) correlation\neffects. While G2 and G3 theory have fairly large errors, G3X theory reproduces\nboth values to within 2 kcal/mol.",
"arxiv_id": "physics/0508076",
"authors": [
"Jan M. L. Martin"
],
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"doi": "10.1016/j.theochem.2006.03.035",
"journal_ref": "J. Mol. Struct. (THEOCHEM) 771, 19-26 (2006)",
"title": "Heats of formation of perchloric acid, HClO$_4$, and perchloric anhydride, Cl$_2$O$_7$. Probing the limits of W1 and W2 theory",
"url": "https://arxiv.org/abs/physics/0508076"
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