A simplified method for theoretical sum frequency generation spectroscopy calculation and interpretation: The "pop...

Area of Science:

• Computational Chemistry
• Spectroscopy
• Surface Science

Background:

• Current theoretical spectra calculations rely on time-correlation functions from atomistic simulations, often ab initio.
• Interpreting these spectra requires deconvoluting contributions from various interfacial populations, lacking a standardized method.
• This complexity hinders the rationalization of experimental spectroscopic data.

Purpose of the Study:

• To develop a more accessible and versatile method for calculating theoretical spectra.
• To simplify the molecular interpretation of spectra by directly linking them to interfacial population statistics.
• To enable accurate spectral predictions for conditions not amenable to direct simulation.

Main Methods:

• Rewriting spectra calculation equations as a sum of partial contributions from interfacial populations, weighted by their abundance.
• Parameterizing Sum Frequency Generation (SFG) signatures from each population into a minimal dataset of reference partial spectra.
• Utilizing interfacial population statistics, calculable from force field simulations or analytic models, for spectral prediction.

Main Results:

• Demonstrated that accurate theoretical spectra can be predicted solely from interfacial population statistics.
• Showcased the ability to parameterize SFG signatures into reference partial spectra for each population.
• Successfully predicted pH-dependent SFG spectra for silica/water interfaces, a condition not directly simulated.

Conclusions:

• The developed approach broadens the range of simulation techniques for theoretical spectra calculation, including non-atomistic and Monte Carlo methods.
• This method significantly simplifies spectral interpretation and rationalization.
• Enables accurate theoretical spectra prediction for challenging interfacial conditions, advancing surface science and computational chemistry.