Fales, B.S.; Seritan, S.; Settje, N.F.; Levine, B.G.; Koch, H.; Martínez, T.J.
J. Chem. Theory Comput., 2018, 14(8), 4139-4150
Full configuration interaction (FCI) is a correlated electronic structure method that takes into account all possible configurations of electrons in all available orbitals; within the approximation of a given basis set, it solves the electronic Schrodinger equation exactly. However, it scales factorially since it takes all combinations of electrons and orbitals. This work presents a rank-reduced formulation of FCI where the wavefunction is built up as a sum of rank one terms. RR-FCI scales better than FCI by a factor of a square root while maintaining a high degree of accuracy and remaining a black box method.
I primarily helped benchmark the RR-FCI method on singlet-triplet gaps in a series of polyacenes and on nitrogen dissociation. I also ran some exploratory calculations studying the rank sparsity of the CI vector, and had minor contributions to the implementation, enabling one to restart RR-FCI calculations.