Portal de Periódicos da CAPES

Breakdown of the Single-Exchange Approximation in Third-Order Symmetry-Adapted Perturbation Theory

2012; American Chemical Society; Volume: 116; Issue: 11 Linguagem: Inglês

10.1021/jp300109y

1520-5215

Ka Un Lao, John M. Herbert,

Molecular Junctions and Nanostructures

We report third-order symmetry-adapted perturbation theory (SAPT) calculations for several dimers whose intermolecular interactions are dominated by induction. We demonstrate that the single-exchange approximation (SEA) employed to derive the third-order exchange–induction correction (Eexch–ind(30)) fails to quench the attractive nature of the third-order induction (Eind(30)), leading to one-dimensional potential curves that become attractive rather than repulsive at short intermolecular separations. A scaling equation for Eexch–ind(30), based on an exact formula for the first-order exchange correction, is introduced to approximate exchange effects beyond the SEA, and qualitatively correct potential energy curves that include third-order induction are thereby obtained. For induction-dominated systems, our results indicate that a "hybrid" SAPT approach, in which a dimer Hartree–Fock calculation is performed in order to obtain a correction for higher-order induction, is necessary not only to obtain quantitative binding energies but also to obtain qualitatively correct potential energy surfaces. These results underscore the need to develop higher-order exchange–induction formulas that go beyond the SEA.