Molecular quantum mechanics, computational methods, molecular properties, and reactivity.
Our research is in the general area of theoretical/computational chemistry. With the aid of detailed calculations of the electronic structure and potential energy surfaces of molecules, we seek to understand their structures, their properties, their relative stabilities, and the changes they undergo during a chemical reaction. In addition to using outside supercomputers, we share a computational laboratory with Professor King’s group.
Our work, much of which is in collaboration with others, involved the development and application of methods for more efficiently carrying out theoretical computations, some of which are outlined below.
The highly popular semiempirical molecular orbital methods are attractive for application to molecules – often fairly large – which resemble those used in the parameterization process. One aspect of our work on these methods is a new, rotationally invariant scheme for generating the electron repulsion integrals required. Computer algebra systems are used to automatically produce the actual formulas. Another aspect is the development of techniques for performing these calculations on a distributed memory parallel computer. Here the essential idea is to find efficient algorithms which involve a minimal amount of exchange of data among the processors while keeping them all busy doing useful calculations. In this regard, we have successfully coded a version of the MNDO semiempirical method for the Intel Hypercube. Our more recent work in semiempirical molecular electronic structure theory is in designing algorithms for rapid geometry optimization, reaction path following, and classical dynamics calculations.
We also study reactions involving singlet and triplet biradicals. These species, which result from the breaking of a covalent bond in a ring, are suspected intermediates in a variety of reactions. The results of our ab initio MCSCF calculations on singlet tetramethylene indicate that its role as an intermediate may be largely due to entropic effects arising from the new internal motions which result from breaking the ring.
The biradical calculations involved the use of Variational Transition State Theory. Computationally, this theory requires the determination of a steepest descent reaction path and the evaluation of parameters in the Reaction Path Hamiltonian. We are developing methods for this evaluation that are well suited for FTST calculations with ab initio MCSCF potential surfaces.