## Large-Scale Electron Correlation Calculations: Rank-Reduced Full Configuration Interaction

journal contribution

posted on 11.06.2018 by B. Scott Fales, Stefan Seritan, Nick F. Settje, Benjamin G. Levine, Henrik Koch, Todd J. Martínez#### journal contribution

Any type of content formally published in an academic journal, usually following a peer-review process.

We present the rank-reduced full
configuration interaction (RR-FCI)
method, a variational approach for the calculation of extremely large
full configuration interaction (FCI) wave functions. In this report,
we show that RR-FCI can provide ground state singlet and triplet energies
within kcal/mol accuracy of full CI (FCI) with computational effort
scaling as the square root of the number of determinants in the CI
space (compared to conventional FCI methods which scale linearly with
the number of determinants). Fast graphical processing unit (GPU)
accelerated projected

**σ**=**Hc**matrix–vector product formation enables calculations with configuration spaces as large as 30 electrons in 30 orbitals, corresponding to an FCI calculation with over 2.4 × 10^{16}configurations. We apply this method in the context of complete active space configuration interaction calculations to acenes with 2–5 aromatic rings, comparing absolute energies against FCI when possible and singlet/triplet excitation energies against both density matrix renormalization group (DMRG) and experimental results. The dissociation of molecular nitrogen was also examined using both FCI and RR-FCI. In each case, we found that RR-FCI provides a low cost alternative to FCI, with particular advantages when relative energies are desired.