The Shee lab develops ab initio electronic structure methods for correlated molecular systems. A fundamental aim is to understand strong correlation and the chemical and physical phenomena that it gives rise to, and we are actively developing scalable electronic structure models to provide quantitative insights into these systems.
Our group's first publication provides an interpretation of "strong correlation" that is physically and mathematically transparent. Correlation is viewed in a statistical sense (as opposed to "correlation energy''), and equated with large values of the trace or square norm of the cumulant of the two-body reduced density matrix. We are working to bridge this fairly abstract concept with physical principles such as group theory and symmetry breaking, and chemical phenomena such as antiaromaticity and superexchange in polynuclear transition metal clusters.
Phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) has demonstrated remarkable accuracy for a wide variety of transition metal-containing systems exhibiting both weak and strong correlations. The low-polynomial scaling of the method's computational cost with system size and its suitability for massive parallelization enable its application to chemical systems beyond the reach of, e.g., coupled cluster models. We are pursuing a number of methodological advances that have the potential to position ph-AFQMC as a true "gold standard" method for ground and excited electronic states, focusing on both energies and properties with the goal of making connections with experiments. A fundamental motivation that pervades much of our current research is to better understand the role(s) of the trial wavefunction, and to understand what the requisite physical properties are of an optimal trial. We are currently exploring various types of trial wavefunctions that are suitable for large strongly correlated systems.
We value and welcome opportunities to collaborate with experimentalists, at Rice and beyond.