DFT modeling of Mn charged states in [Ga.sub.1-x][Mn.sub.x]As diluted ferromagnetic semiconductors: the cluster approach

Quantum chemical cluster modeling of the high-symmetry nanoclusters [Ga.sub.15]Mn[As.sub.16][H.sub.36] and [Ga.sub.12]Mn[As.sub.16][H.sub.36] simulating the bulk of a GaAs crystal with Mn paramagnetic impurity center is carried out within the Density Functional Theory. A Generalized Gradient Approximation method PBEPBE/LanL2DZ is used to study the neutral [Mn.sup.0] and ionized [Mn.sup.-] states of a Mn atom in the nanoclusters under consideration. The change of the charge state of the impurity center from [Mn.sup.0] to [Mn.sup.-] leads to a considerable relaxation of Mn-As bonds in the immediate surroundings of the Mn atom and to the "p-hole" recombination. It also affects the spin density localization. The components of the g-tensor for both the neutral [Mn.sup.0] and the ionized [Mn.sup.-] states are calculated by the Gauge-Independent Atomic Orbital (GIAO) method with the hybrid density-functional mPW1PW91. The resulting values of the g-factor are in good agreement with the experimental Electron Paramagnetic Resonance data. The results obtained confirm the applicability of the cluster approach for describing charge effects in dilute ferromagnetic semiconductors. DOI: 10.1134/S1063782614080168