Several computational techniques have been developed for simulating sum frequency generation spectroscopy (SFG). Using time-dependent wavepacket dynamics to describe vibronic coupling, we can predict the orientation of molecules at interfaces for doubly-resonant SFG. This implementation includes theory to both describe the Franck-Condon (FC) approximation, as well as higher order Herzberg-Teller (HT) terms. The FC approximation is not satisfactory and incorporation of HT terms is necessary to properly predict the SFG spectrum. In addition, a polarizable quantum mechanics/molecular mechanics method has been applied to describe SFG of molecules adsorbed onto metal nanoparticles using the short-time approximation. This approach treats the nanoparticle atomistically which allows the capture of the microscopic structure of the nanoparticle. Large signal enhancements are observed due to coupling between the nanoparticle's surface plasmon and the molecular vibrational modes.

Theoretical applications of sum frequency generation: Determining molecular orientation of complicated systems

246th National Meeting (2013)

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