A polarizability driven ab initio molecular dynamics approach to stimulating Raman activity: Application to C₂₀

Abstract

We describe a novel variant of the driven molecular dynamics (DMD) method derived for probing Raman active vibrations. The method is an extension of the conventional μ-DMD formulation for simulating IR activity by means of coupling an oscillating electric field to the molecule’s dipole moment, μ, and inducing absorption of energy via tuning the field to a resonant frequency. Presently, we modify the above prescription to invoke Raman activity by coupling two electric fields, i.e. a ‘Pump’ photon of frequency ω_P and a Stokes photon of frequency ω_S to the molecule’s polarizability tensor, α, with the difference in the frequencies ω = ω_P – ω_S corresponding to the Stokes Raman shift. If ω is close to a Raman active vibrational frequency, energy absorption ensues. Varying ω allows identifying and assigning all Raman active vibrational modes, including anharmonic corrections, by means of trajectory analysis. We show that only one element of the full polarizability tensor, and its nuclear derivative, is needed for an α-DMD trajectory, making this method well suited for ab initio dynamics implementation. Numerical results using first-principles calculations are presented and discussed for the vibrational fundamentals, combination bands, overtones of H₂O, CH₄, and the C₂₀ fullerene.

GRAPHICAL ABSTRACT

KEYWORDS:

• Driven molecular dynamics
• polarizability tensor surface
• stimulated Raman excitation
• molecular vibrations
• electronic structure theory

Acknowledgements

This work was also supported in part by research computing resources and technical expertise via a partnership between Kennesaw State University’s Office of the Vice President for Research and the Office of the CIO and Vice President for Information Technology [49].

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This material is based upon work supported by the National Science Foundation under Grant No. (CHE-1855583, DUE-1623723).