We have developed the spin-unrestricted divide-and-conquer (DC)-based linear-scaling self-consistent field method for treating open-shell systems (Kobayashi et al. in Chem Phys Lett 500:172, 2010). Because the method does not require the position of excess spins or charges, it made the treatment of large spin-delocalized systems tractable. The present study extends the DC-based unrestricted open-shell scheme to the correlated second-order Møller-Plesset perturbation (MP2) theory. Numerical applications to polyene cations demonstrate that the present method gives highly accurate results with less computational costs even for spin-delocalized systems.
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