Hi
i am Dhanya, a research scholar from kerala university.
i am studying non- linear optical properties of a set of compounds using DFT with functional B3LYP and basis set 6311G (d p)using Gaussian 09 software. Upto my knowledge i believed that if a compound having good NLO properties, it has low HOMO - LUMO gap and high hyperpolarizabilities.
i calculated HOMO - LUMO gap and hyperpolarizabilities. But in the case of set of compounds of my study, the decreasing of HOMO - LUMO gap and increasing of hyperpolarizabilities are NOT IN SAME ORDER.
What should i do?
please help me🙏😔
Although it is true that compounds with a narrow HOMO-LUMO gap often display large hyperpolarizabilities (beta) and hence second-order NLO properties, the HOMO-LUMO gap is not directly proportional to hyperpolarizability and therefore it is not expected to follow the same trend.
So if you are interested in NLO you have to calculate beta values, there are no shortcuts. In Gaussian this can be done within a vibrational analysis (freq=Raman). I and my coworkers have published a couple of papers regarding NLO properties of metal complexes. An example is this: Article Structure-Property Relationships in PtII Diimine-Dithiolate ...
I hope this may help.
The existence of first-order molecular hyperpolarizability suggests that the designed molecule possess the NLO properties while it doesn't have to be aligned with HLG gap order.
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