Abstract
Invited for this month′s cover picture are Dr. Tárcius N. Ramos and Prof. Benoît Champagne at the University of Namur (Belgium). The cover picture shows the interfacial selectivity of second harmonic generation at the water‐vacuum interface, which is targeted in this work. In more details, the molecular first hyperpolarizability responses have been calculated by combining classical molecular dynamics and quantum chemistry simulations, and our model was able to distinguish between the bulk and the interfacial contributions. Read the full text of their Research Article at 10.1002/open.202200045.
“… The orientation of the polarization induced by the explicit surrounding water molecules is essential for describing interfacial second harmonic generation studies….” Find out more about the story behind the front cover research at 10.1002/open.202200045.
What is the most significant result of this study?
We have simulated the first hyperpolarizability of water clusters belonging to different molecular layers of the air‐water interface using the sequential molecular mechanics/quantum mechanics approach. The surrounding molecules are shown to tune the linear and nonlinear optical responses of the target cluster. Thus, the evaluation of different embedding models was the main topic of this study. Yet, distinguishing the interfacial and bulk first hyperpolarizability responses was only achieved provided one uses a polarizable embedding model corrected with an effective external field to represent the surrounding water molecules.
What prompted you to investigate this topic/problem?
Nonlinear optical spectroscopies are efficient techniques to characterize interfaces because, by nature, they are non‐centrosymmetric and therefore they exhibit first hyperpolarizability responses. Recently, theoretical water‐vacuum interfacial second harmonic generation has received more attention, and several studies investigating this region have emerged. However, none of them have systematically investigated different embedding models.
What are the main challenges in the broad area of your research?
The orientation of the polarization induced by the explicit surrounding water molecules is essential for describing interfacial second harmonic generation studies. Discrete solvation methods are reliable for investigating this region because the anisotropic surrounding effects are explicitly included. As reported in the present study, the embedding model should be carefully chosen. Moreover, the connection between the microscopic and macroscopic responses remains weakly established.
Ramos T. N., Champagne B., ChemistryOpen 2023, 12, e202200248.