Quantum Monte Carlo study of electron correlation in chromium-doped silicon cluster Cr@Si₁₂

Electron correlation in chromium-doped silicon cluster (Cr@Si₁₂) in its neutral, positively, and negatively charged states with different nuclear configurations is investigated by means of quantum Monte Carlo methods. It is found that the correlation energy per electron is independent of whether the state is charged or not and about -1 eV for each of these three states. The total binding energy of the neutral state per atom is 3.5 eV, which is divided into the Hartree-Fock contribution nearly equal to 1.2 eV and the correlation contribution as large as 2.3 eV. In the Hartree-Fock approximation, the ionization energy is 6.9 eV and the electron affinity is 2.7 eV. Correlation increases the ionization energy by 1.7eV and the electron affinity by 1.4eV.