Extended Hückel and Slater’s rule initial guess for real space grid-based density functional theory

Abstract

The Extended Hückel method is commonly used as an initial guess for Gaussian basis set quantum chemistry calculations. In this work, we combine the Extended Hückel method and Slater’s rules to form an initial guess of the electron density and molecular orbitals for all-electron real-space finite element Kohn–Sham density functional theory (FE-KSDFT). With this approach, the first SCF iteration is close in energy to the converged solution, and a factor of two speedup is obtained vs. a naïve initial electron density composed of a superposition of atomic densities. In addition, because the guessed molecular orbitals are already partially self-consistent with the guess density, we can now employ less robust, but fast, block eigensolvers such as Chebyshev-filtered subspace iteration even in the first SCF iteration to achieve 2–10× further gains vs. a conventional Jacobi–Davidson eigensolver.