Ab Initio Calculation of Accurate Molecular Wave Functions

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This project to develop geminal-based methods in molecular electronic structure theory is supported jointly by the NSF Theoretical and Computational Chemistry Program and the the Advanced Scientific Computing Division. Methods will be developed for the computation of accurate, ab initio, small molecule, electronic wavefunctions using contracted Gaussian geminals (predetermined linear combinations of explicitly-correlated, two-particle, Gaussian basis functions). Geminal parameters for molecules will be extracted from optimized atomic wavefunctions. Scalable algorithms will be developed for implementation on parallel computers. The quantum mechanical electronic wavefunction is a mathematical function of the spatial and spin coordinates of all the electrons in the atom or molecule. These many-body functions are traditionally expressed in terms of orbitals, i.e. functions of the coordinates of a single electron. Orbital-based concepts and computational methods play a central role in modern chemical theory, but there is a practical limit to the accuracy attainable in orbital-based computations using existing supercomputers. The goal of this project is to develop improved computational methods using geminals (explicit functions of the coordinates of a pair of electrons) rather than orbitals. If successful, this will significantly increase the accuracy of theoretical predictions of gas phase reaction rates such as those required for improved computer models of the earth's atmosphere.