A hierarchy of composite quantum chemical models for applications in materials and surface Chemistry

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Krishnan Raghavachari is supported by an award from the Chemical Theory, Models and Computational Methods program to develop a set of hierarchical quantum chemical methods for state-of-the-art applications in materials and surface chemistry. The hierarchical concept involves the use of highly accurate methodology on small systems to validate more approximate and computationally cost effective methodologies for investigating complex systems. Building on prior work in the PI's research group, Raghavachari and coworkers are developing more sophisticated and broadly applicable methods in three areas: (1) The "connectivity-based-hierarchy", an accurate thermochemical method for medium-sized organic and biomolecules, will be developed for radicals and ions, and calibrated for applications involving amino acids and peptides; (2) New energy and gradient methods including electronic embedding and charge transfer effects will be developed for an accurate QM/QM embedding model based on the successful ONIOM framework; (3) Efficient analytical gradients will be developed for a generalized multilayer "molecules-in-molecules" fragment-based method including electronic embedding . These developments will be used in a range of applications on silicon and silica surfaces as well as for investigating biomolecular systems such as peptides.Accurate treatment of complex systems is one of the main challenges in quantum chemistry. The new methods being developed will fill a critical need to treat medium-sized and large molecules accurately, providing systematic well-tested models for the study of materials and surface systems. The computer codes developed in this program will be available to the scientific community as part of the Gaussian software package as well as in a set of freely available codes on the PI's website. The methods are expected to be widely used by a broad range of investigators. The project involves both method development and applications, and will provide an excellent opportunity for training the next generation of researchers in quantum chemistry