{"id":441,"date":"2015-12-23T05:35:48","date_gmt":"2015-12-23T05:35:48","guid":{"rendered":"http:\/\/wtheiss.com\/wordpress\/?p=441"},"modified":"2015-12-23T06:20:36","modified_gmt":"2015-12-23T06:20:36","slug":"model-selection","status":"publish","type":"post","link":"https:\/\/wtheiss.com\/wordpress\/?p=441","title":{"rendered":"Model selection"},"content":{"rendered":"<p><strong>How do I select the right model for the optical constants?<\/strong><\/p>\n<p>Selecting appropriate optical constant models with the right number of parameters is difficult and requires some experience. The choice depends &#8211; first of all &#8211; on the material and also on the spectral range of interest.<\/p>\n<p>In the infrared the choice is rather easy: Use a constant refractive index, and add for each clearly visible vibrational mode a Kim oscillator. If you have free charge carriers (i.e. you deal with a metal or a doped semiconductor) you should add a simple Drude model (in case of highly doped semiconductors use an enhanced Drude model instead).<\/p>\n<p>In the NIR, visible or UV the right choice is not so simple. Here you can be guided by the following rules of thumb:<\/p>\n<p>Metals:<br \/>\nUse a constant to represent high energy interband transitiions. For every interband transition causing structure in the wanted spectral range use a Tauc-Lorentz or an OJL term. Take a Drude model for the free electrons.<\/p>\n<p>Semiconductors (crystalline):<br \/>\nCombine a constant and Tauc-Lorentz terms for interband transitions. Add a Drude model for low doped materials. In the case of high doping levels use an extended Drude model.<\/p>\n<p>Semiconductors (amorphous):<br \/>\nSetup a model like for crystalline semiconductors (see above) but replace the Tauc-Lorentz terms by OJL terms.<\/p>\n<p>Oxides and Nitrides:<br \/>\nCombine a constant and an OJL term. If the OJL term alone cannot generate the right absorption and dispersion, you should add a harmonic oscillator in the far UV (resonance frequency 60000 1\/cm, oscillator strength in the range 10000 &#8230; 100000 1\/cm, damping 1 1\/cm). In the fitting procedure the harmonic oscillator parameters should be kept fixed with the exception of the oscillator strength.<\/p>\n<p>Organic materials:<br \/>\nCombine a constant, an OJL model and Kim oscillators. Whereas the OJL model is used to describe the &#8216;fundamental absorption&#8217; in the UV, the Kim oscillators should represent absorption bands in the visible and NIR.<\/p>\n<p>!!! Please note that OJL and Tauc-Lorentz terms may not be inserted in the susceptibility list as the other models. Instead, they have to be used within a KKR susceptibility object. !!!<\/p>\n","protected":false},"excerpt":{"rendered":"<p>How do I select the right model for the optical constants? Selecting appropriate optical constant models with the right number of parameters is difficult and requires some experience. The choice depends &#8211; first of all &#8211; on the material and also on the spectral range of interest. In the infrared the choice is rather easy: [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[10],"tags":[15,12,14,11,16,17],"_links":{"self":[{"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/441"}],"collection":[{"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=441"}],"version-history":[{"count":1,"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/441\/revisions"}],"predecessor-version":[{"id":442,"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/441\/revisions\/442"}],"wp:attachment":[{"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=441"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=441"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wtheiss.com\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}