# Non Linear optical Coefficient

Hello everyone:
I am a newbie in Quantum Chemistry and I want to do some calculation on some physical properties such as the title shows. However, as we know, lots of package can't give you exactly what you want,you have to tackle with some succeeding process to get a beatiful result which may be used in your paper. There is the question: how can I get non-linear optical coefficient from results of calculation by, for example, GAUSSIAN? And is there anyone who is familiar with it and may give me some help? More thanks.

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I think this question is too technical for this forum. I have never worked with GAUSSIAN. Maybe it can be used to calculate polarizabilities, maybe also to higher orders (second order should be zero for free atoms).

Please, can you define the non-linnear optical coefficient? Are you talking about the higher order susceptibilities?

Gonzolo
I believe I am familiar with this sort of thing, but I don't understand the question:

"how can I get non-linear optical coefficient from results of calculation by, for example, GAUSSIAN?"

Gaussian what? Calculate susceptibilities (?) from what?

While I've never done such calculations (nor do I have much experience with GAUSSIAN), I am somewhat familiar with them. Generally what one does is break down the desired end results into more easily calculable parts (e.g., in this case, you'd likely have to compute dipole moments, among other things) and then "put it together" in accordance to whatever approximations one has made.

There are a number of computational/theoretical papers out there (I'd go check the archives of J. Chem. Phys., Chem. Phys. Lett., and the like) where one can find the groundwork, and the GAUSSIAN manual for the implementation. I know Bill Goddard (among others) has done these sorts of calculations for organic materials, and it seems like there's at least one of these sorts of papers every issue for things like semiconductors and other inorganic materials.

sorry for my unclearness, and thanks for your kind reply. Here I want to make it more clear: what I want to know is that how one can get 2-order or 3-order non-linear optical coefficient(is this need definition?) of an organic molecular through calculation result by GAUSSIAN98/03?-because I can't tell what is useful from the output of GAUSSIAN and I don't know how to get the coefficients from the very result. I have read some paper but they only said the methods( for example MP2) and the result(concrete value of the coefficient) and I can't get to know the intermediate process, thus there is the question. I hope one can tell me the process--may be exactly on how one
"break down the desired end results into more easily calculable parts (e.g., in this case, you'd likely have to compute dipole moments, among other things) and then "put it together" in accordance to whatever approximations one has made. "(quoted from Mike)
and its physical ground or refer me to some papers or books.

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