ISSN:
0020-7608
Schlagwort(e):
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Binding energies for complexes of N2O with the acids H+, Li+, and HF have been computed using the following correlation methods: many-body (Møller-Plesset) perturbation theory at second (MP2), third (MP3), and fourth (MP4) order; the “quadratic CI” method with single and double excitations (QCISD) and with noniterative inclusion of triple excitations (QCISD(T)); the linearized coupled-cluster method (LCCM); the averaged coupled-pair functional (ACPF); configuration interaction with all single and double excitations (CISD); and CISD with the Davidson and Pople corrections. The convergence of the Møller-Plesset expansion is erratic, predicting that the terminal nitrogen is the preferred binding site for the complexes at the MP2 and MP4 levels, in disagreement with Hartree-Fock and MP3 and all other models (including the infinite-order QCI). The effect of triple excitations at MP4 and QCI is to destabilize complexes bound at O and stabilize those bound at N, but this effect is greatly overestimated at MP4 relative to QCI. Except for the LCCM result for N-protonated N2O, ACPF and LCCM bindin energies are similar to the QCISD values. The size-consistency error in the ACPF binding energies of the complexes of N2O with HF is about 0.5 kcal/mol. The CISD size-consistency error for these complexes is 23 kcal/mol, leading to negative binding energies when computed relative to isolated N2O and HF. The Davidson correction reduces the size-consistency error but still leaves the binding energies negative. The Pople correction produces positive but too small binding energies. However, all methods give consistenly good, essentially indistinguishable binding energies when computed relative to a similar calculation on a supermolecule of infinitely separated N2O and HF units. Multireference ACPF and CISD binding energies have also been obtained using MCSCF reference functions which correlate the highest occupied and lowest virtual pairs of π orbitals. The multireference binding energies are not greatly different from the single-reference values, and do not reverse the negative binding energies of the complexes with HF at the CISD level when computed relative to isolated molecules. When calculated relative to the infinitely separated supermolecule, the multireference binding energies of these complexes are virtually identical to the corresponding single-reference values.
Zusätzliches Material:
7 Tab.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/qua.560382445
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