“…Examples include BaGa 4 S 7 , 8 BaGa 4 Se 7 , 9 BaGa 2 MSe 6 (M = Si, Ge; Q = S, Se), 10 Pb 4 Ga 4 GeQ 12 (Q = S, Se), 11 Ba 23 Ga 8 Sb 2 S 38 , 12 Cs 5 BiP 4 Se 12 , 13 Ln 4 GaSbS 9 (Ln = Pr, Nd, Sm, Gd−Ho), 14 and Ba 2 InYQ 5 (Q = Se, Te), 15,16 LiGaS 2 , 17 LiGaSe 2 , 18 Li 2 In 2 MS 6 (M = Si, Ge), 19 SnGa 4 Q 7 (Q = S, Se), 20 AAsQ 2 (A = Li,Na; Q = S,Se), 21 AZrPSe 6 (A = K, Rb, Cs) 1 and Na 4 MgM 2 Se 6 (M = Si, Ge). 22 Generally speaking, a large macroscopic NLO response originates from the cooperative arrangement of the microscopic NLO building units, including the MX 4 tetrahedra (M = Ga, In, Si, Ge, Sn etc.…”