Divide-and-conquer self-consistent field calculation for open-shell systems: Implementation and application

In this Letter, the divide-and-conquer (DC) linear-scaling self-consistent field method is extended to the spin-unrestricted Hartree-Fock (UHF) method or Kohn-Sham density functional theory (UDFT) for treating large open-shell systems. Although the DC method is one of the fragmentation-based linear-scaling schemes, the present DC-UHF/UDFT framework can avoid specifying the number of up- and down-spin electrons in each fragment by introducing up- and down-spin Fermi levels. Test calculations for oligothiophenes demonstrate the high efficiency and accuracy of the DC-UHF/UDFT method even for spin-delocalized systems.