| Summary: | 碩士 === 淡江大學 === 物理學系 === 90 === Electronic and band structure calculations of various semiconductors, insulators, oxides and molecules are performed. We have slightly modified a version of so-called Generalized DFT (GDFT) method to correct the band gap, i.e. to evaluate the scissors correction. It seems to provide an acceptable improvement on the band gap of a wide range of semiconductors, insulators, oxides as well as molecules. The importance of this method become obvious when DFT based computational approach is used to study optical properties of new or not-yet existing materials, because in those cases the actual gaps are not known.
Visible and UV lasers have been widely used in medical, industrial and entertainment applications. A probable way to obtain these lasers is to use nonlinear optical (NLO) crystal to produce second harmonic laser frequency. Searching for a new NLO crystal is very important. GdCa4O(BO3)3 (abbreviated as GdCOB) had grown by Iwai, Kobayashi, Furuya, Mori and SaSaki in 1997. For our experience in studying LBO (LiB3O5), BBO (BaB2O4), CBO (CsB3O5) and CLBO (CsLi(B3O5)2), the anionic group plays the most important part in nonlinear optical properties. We combining the plane-wave pseudopotential calculation and partial density of state (PDOS) analysis techniques to study GdCOB crystal.
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