利用第一原理計算A位陽離子取代非線性材料AGeX 3 之光學性質

Abstract

利用第一原理計算在A位陽離子取代非線性光學晶體AGeX3(X=Cl,Br)時光學之特性,我們嘗試使用K,Cs,Rb陽離子與GeX3陰離子團結合,並藉觀察陽離子取代改變晶體結構,電子能帶結構,二倍頻係數,晶胞基態總能等參數,期望能找出最合適使用之非線性光學晶體. 利用化學合成法生長三元鹵化物AGeX3(X=Cl,Br),甚至是四元鹵化物CsRbGeX3,並藉FTIR,Raman光譜,X光繞射光譜及二倍頻粉末量測實驗,期望能配合理論計算之結果,能找到設計晶體之最佳組合。

By substitution of A site cation in a nonlinear crystal CsGeCl3 or CsGeBr3 we hope to find the property of the new crystal through the first principle calculations. K＋,Rb＋,Cs＋ are those cations together with anions being formed as the new crystals. Through calculation several parameters of the new crystal such as crystal structure, ground state total energy, bulk modulus, electronic band energy, second order nonlinear coefficients and so on can be found. We hope to obtain some important information from calculation in finding an useful nonlinear crystal. Besides, ternary halide crystal AGeX3 (A=Cs, Rb, K; X=Cl, Br) or even quarternary halide RbxCs1-xX3 could be obtained if chemical synthetic technique are used. From experimental measurements, FTIR、Raman spectrum、X ray diffraction pattern、powder SHG、and absorption spectrum, we can modify our theoretical model and give the correct results.