Dear SIESTA users, I'm trying to investigate influence of Ni substitutional impurity on electronic properties of strongly anisotropic semiconducting ferroelectric crystal SbSI with orthorhombic symmetry.
In my investigations I substitute one Sb atom (which behaves in the host crystal like Sb 3+ ion, electron configuration 5s°2 5p°3) on one Ni atom in different supercells. As it follows from the experiment Ni atom ( in the amount of 2 mol.%) behaves in the host crystal like Ni 2+ ion (symbolic configuration is d°8). As far as I know when transition atom with electron configuration d°p s°q substitutes trivalent ion (e.g., Ga in GaP), its oxidation state is T 2+, if it behaves like singly negative impuritiy with charge -1 and its formal configuration is d°N=d°(p+q-2). So, I suppose that in my case Ni 2+ behaviour of transition atom also corresponds to singly negative charged state with formal configuration d°8, doesn't it? Am I right? If so, should I introduce NetCharge equel to -1, while conducting calculations of ground state in the supercell approximation? Does SIESTA consider the NetCharge also for non-cubic systems like in my case? Or should I make supercell calculations without introducing NetCharge into the system and obatine d°8 formal electron configuration from Mulliken population analysis? If I don't take into consideration NetCharge, does it strongly change the result on band structure and DOS calculations? I have also investigted the vacancy electronic properties simply withdrawing one Sb atom. What is the charge state of vacancy in this case? If it is charged, should I take into account NetCharge backgroud in this case? I will appreciate any help very much. Thank you very much in advance. Best regards, Ivetta
