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Dispersion Corrected Functional Density Methods

The density functional theory is generally used to model strong intermolecular interactions between solid macromolecular systems, including thermochemistry and covalent bonding. However, the description of long range dispersion interactions is not always accurate. Methods for applying the density functional theory to include dispersion correction are under constant development and, as of the date of publication, include nonlocal van der Waal, conventional and parameterized, semiclassical corrections, and one-electron corrections.

  1. Functional Density

    • The density functional theory has largely been successful in describing the ground state properties of semiconductors, insulators and metals, and also includes complex materials such as carbon nanotubes and proteins. Instead of many-body wave functions, the theory uses density to describe the interacting system of fermions. Functional density is practically applied according to approximations made for the exchange-correlation potential, which provides further explanation of the Pauli principle and Couloumb potential effects, far beyond an electrostatic electron interaction.

    Dispersion Interactions

    • Dispersion interactions are the attractive portions of long range van der Waal forces between indirectly bonded atoms and molecules. They serve an important function in molecular electronics, biological systems, molecular crystals and energetic materials. To achieve chemical accuracy when modeling large systems, dispersion interactions must be included. Current methods use a super-molecular calculation of the total energy of the system, and obtain the interaction energy from a performed fragment.

    Nonlocal Van der Waal and Parameterized Methods

    • The nonlocal van der Waal Method computes dispersion energy in a non-empirical way, based on their electron density. The advantage of this method is that dispersion effects are incorporated naturally by way of the charge density, thus dispersion dependence on atomic oxidation state is included automatically. Parameterized methods are applied to equilibrium structures of medium-sized molecules. Their major drawback is numerical instability, which leads to noisy potential energy curves and artificial van der Waal minima.

    Semiclassical and One-electron Corrections

    • The semiclassical method dates back to the '70s and is modified based on treatment of dispersion energy with atom pairwise additives. This improves accuracy and applicability and reduces empiricism. Upgraded methods also allow the easy calculation of energy gradients for efficient geometry optimization. The one-electron method utilizes atom-centered nonlocal potentials and is typically applied to modeling van der Waal forces in graphite, benzene and argon complexes. The potentials used, however, decay quickly with increased inter-atomic distance.

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