Symmetry Projected Coupled Cluster Theory

William Marsh Rice University, Houston TX

Investigators

Abstract

Gustavo Scuseria of William Marsh Rice University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop accurate and affordable computational methods for challenging molecules. The systems of interest have several electrons that influence each other in ways that lead to many states with similar energies. Systems of this type are called "strongly-correlated" and can exhibit novel properties which have the potential to spur technological advancement in a number of fields. However, these systems are challenging to theoretically describe and are often intractable for current computational methods. Professor Scuseria's group is developing a new approach that is accurate and can be applied to large, realistic systems, all the while giving superior results for strongly correlated systems. The researchers are working both to continue to develop the new approach and to apply the method to important systems like transition-metal clusters and polycyclic aromatic hydrocarbons in order to provide useful insights into technologically-relevant systems. Dr. Scuseria is involved in outreach activities in the Houston area. Specifically he is organizing events with the Latin American Graduate Student Association at Rice University. He provides informal advice about job opportunities in academia as well as in industry. Dr. Scuseria is also involved in the Rice Science Cafe, where ideas about science and technology are discussed with the general public. Strong correlations are ubiquitous and technologically important, but unfortunately cannot be accurately described except by a handful of computational approaches. One of the more promising approaches for the treatment of strong correlation is the use of symmetry projection, i.e. recovering the symmetry-preserving component of a broken-symmetry wavefunction. Symmetry projection is black box, and symmetry projected mean-field methods can be applied to systems with dozens or even hundreds of strongly correlated electrons. In order to reach quantitative accuracy for strongly-correlated systems, the Scuseria group is working to extend their symmetry projected mean-field methods to symmetry projected coupled cluster theory. This theory combines the advantages of symmetry projection for the description of strong correlation on the one hand with coupled cluster theory for the description of weak correlation on the other, becoming a form of black-box multireference coupled cluster theory. The new approach has the potential to efficiently and reliably treat weak and strong correlations on equal footing while affording the straightforward computation of properties and other expectation values. While the Scuseria group continues to develop and extend symmetry projected coupled cluster theory, their current applications of the approach are strongly correlated systems which display spin frustration and accompanying magnetic order, which should provide valuable insights for future technological development. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.