Improvement of initial guess via grid-cutting for efficient grid-based density functional calculations

Abstract

We introduced an efficient initial guess method, namely the grid-cutting, which is specialized for grid-based density functional theory (DFT) calculations. It produces initial density and orbitals through pre-DFT calculations in an inner simulation box made by cutting out the outer region of a full-size one. To assess its performance, we carried out DFT calculations for small molecules included in the G2-1 set and two large molecules with various combinations of mixing and diagonalization conditions, relative size of the inner box, and grid spacing. For all cases, the grid-cutting method was more efficient than conventional ones such as extended Huckel, superposition of atomic densities, and linear combination of atomic orbitals. For instance, it was about 20% faster in computational time and about 45% smaller in the number of self-consistent-field cycles than the superposition of atomic densities because it provided high-quality initial density and orbitals closer to the corresponding fully converged values. In addition, it showed good performance for non-Coulombic model systems such as harmonic oscillator.