Quadratically convergent algorithm for fractional occupation numbers in density functional theory

A quadratically convergent algorithm for closed shell systems containing orbitals with fractional occupation numbers (QC-FON SCF) is presented. The method successfully finds a minimum on very shallow electronic energy surfaces and achieves rms density matrix convergence of 10^-8 a.u. with 4 Newton steps and 40-60 Fock matrix updates. The benchmark cases demonstrate the most important features of the algorithm. Among methods presently available for FON convergence QC-FON is both fastest and the most general.