Hi Ahmet, > > I am trying to obtain the band structure of Ammonium > Hexafluorosilicate-(NH_4)_2SiF_6-where the space group is Fm3m, > location and occupancies* of the base atoms are: > > atom position occupancy > ------------------------------------------------------------------------ > Si (0,0,0) 1 > F (0.2011,0,0) 1 > N (0.25,0.25,0.25) 1 > H (0.168,0.168,0.269) 1/3 > > When the structure is contructed via symmetry operations, the number > of the H atoms are three times the actual value. Could you please help > me in how to use the knowledge of "occupancy" of the H atoms so that > the band structure calculation gives results corresponding to the > physical structure?
Occupancies are usually not a direct input for electronic structure calculations. To simulate the occupancies one just reduces the number of atom in the structure by hand, I mean deleting those atoms that are not supposed to be there. Sometimes it is obvious what sites should be occupied or empty, for example when H ions are very close to each other. However if it is not the case then you should generate all the non-equivalent possibilities of having 1/3 of the H positions empty and fully relaxed them under the same computational conditions to find the most stable configuration(s). Lazaro -- ============================================================= Lazaro Calderin Department of Physics Queen's University, Kingston, Ontario, Canada E-mails: calderin at physics.queensu.ca
