Graham Fletcher is a Principal Project Specialist in Computational Science at the ALCF with a background in quantum chemistry and supercomputing. His research interests focus on the development of highly scalable methods and algorithms for the accurate and reliable prediction of chemical phenomena. He earned his Ph.D. (physics) from the University of York, UK, under Graham Doggett, who worked with Coulson on molecular orbital theory. Graham has extensive experience in high performance computing, and has worked at Iowa State University, NASA Ames Research Center, and Daresbury Laboratory in the UK. More recently, he is the originator of the Variational Subspace Valence Bond (VSVB) method [1].

VSVB is a rigorous ab initio electronic structure method based on overlapping linear combinations of atomic orbitals (OLCAO). To unlock the benefits of OLCAO, VSVB uses a technique that obviates the famous ‘N! problem’ – the long-standing limitation of overlapping orbitals. The naturally localized orbitals correspond to intuitive chemical objects such as bonds and lone pairs, allowing VSVB to model many classes of chemical problem in a single method: ground and excited states; open- and closed-shell systems; bond-breaking/formation; resonance; etc. VSVB’s ability to represent chemical hybridization leads to a wave function-structure relationship allowing high quality VSVB wave functions to be generated at negligible cost. In addition, VSVB is embarrassingly parallel, with sub-cubic complexity, and linear memory. 

[1] Graham D. Fletcher, "The variational subspace valence bond method", J. Chem. Phys. 142, 134112 (2015). http://dx.doi.org/10.1063/1.4916743