Development of constraint algorithm for the number of electrons in molecular orbitals consisting mainly 4f atomic orbitals of rare-earth elements and its introduction to tight-binding quantum chemical molecular dynamics method

Our original tight-binding quantum chemical molecular dynamics code, "Colors", has been successfully applied to the theoretical investigation of complex materials including rare-earth elements, e.g., metal catalysts supported on a CeO₂ surface. To expand our code so as to obtain a good convergence for the electronic structure of a calculation system including a rareearth element, we developed a novel algorithm to provide a constraint condition for the number of electrons occupying the selected molecular orbitais that mainly consist of 4f atomic orbitals of the rare-earth element. This novel algorithm was introduced in Colors. Using Colors, we succeeded in obtaining the classified electronic configurations of the 4f atomic orbitais of Ce⁴⁺ and reduced Ce ions in a CeO₂ bulk model with one oxygen defect, which makes it difficult to obtain a good convergence using a conventional first-principles quantum chemical calculation code.