Recent Research Developments
Index of Recent Research News
April 14th, 2004
    Design and application of a multi-coefficient correlation method for dispersion interactions

    The modeling of dispersion forces is of considerable interest in chemical physics and biomolecular simulations.  However, accurate quantum mechanical calculation of dispersion forces is extremely challenging owing to the large basis sets and high degree of electron correlation required for their description.  Hartree-Fock and conventional density-functional quantum models have traditionally been unsatisfactory, and higher-level ab initio methods such as high-order perturbation theory or coupled cluster approaches can only be applied to very small systems due to large computational requirements.

    Recently, graduate student Timothy Giese and Prof. Darrin York of the Department of Chemistry have designed a new quantum method for accurate determination of dispersion interactions.   The method is know as a multi-coefficient correlation method for van der Waals (MCCM-vdW) interactions that utilizes the transferability of basis set and electron correlation effects to derive a model that captures dispersion effects at a fraction of the computational cost of other comparably accurate quantum methods.  The method does not require use of so-called "counterpoise corrections", and agrees extremely closely with both experiment and high-level quantum results (Fig. 1).
FIG. 1. A comparison of the fitted MCCM vdW potentials with the reference potentials [J. Chem. Phys. 120, 590 (2004)].
FIG. 2.  (Top) He···H2O potential energy surfaces calculated with a high-level reference, MCCM-vdW and MP3 methods.  (Bottom)  Comparison of classical, quantum-corrected and experimental second virial coefficients. Taken from [Int. J. Quantum Chem. 98, 388 (2004)].

The method can be used for determination of potential energy surfaces such as rare-gas probes used to derive dispersion potentials for molecular simulation force fields (often performed at the MP2 or MP3 levels that are considerably less accurate), properties such as second virial coefficients (Fig. 2), and many-body interaction potentials.   The method opens the door toward the reliable calculation of dispersion interactions of larger systems that may provide benchmark data used to design new, extremely fast and accurate semi-empirical quantum models for hybrid quantum mechanical/molecular mechanical simulations of biological reactions.
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Next scheduled update: Apr. 28, 2004.
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