We present a formulation of Raman spectroscopy in molecular junctions based on a many-body state representation of the molecule. The approach goes beyond the previous effective single orbital formalism and provides a convenient way to incorporate computational methods and tools proven for equilibrium molecular spectroscopy into the realm of current carrying junctions. The presented framework is illustrated by first principle simulations of Raman response in a three-ring oligophenylene vinylene terminating in amine functional groups (OPV3) junction. The calculated shift in Stokes lines and estimate of vibrational heating by electric current agree with available experimental data. In particular, our results suggest that participation of the OPV3 cation in Raman scattering under bias may be responsible for the observed shift, and that the direction of the shift depends on renormalization of normal modes. This work is a step toward atomistic quantum ab initio modeling of the optical response of nonequilibrium electronic dynamics in molecular junctions.

We consider the effects of dephasing on field-induced coherent charge and energy transport in molecular junctions. Within generic models we show that dephasing controls the relative intensities of energy and charge fluxes, and that the dependence of the energy flux on the dephasing rate is nonmonotonic. We further demonstrate the possibility for laser-controlled charge-energy separation in multiterminal molecular junctions, a prerequisite for engineering low-heating stable nanoscale devices. © 2013 American Physical Society.

Theoretical tools employed in ab initio simulations in the field of molecular electronics combine methods of quantum chemistry and mesoscopic physics. Traditionally these methods are formulated in the language of effective single-particle orbitals. We argue that in many cases of practical importance a formulation in the language of many-body states is preferable. We review methods of the nonequilibrium atomic limit and our contributions to their development and applications. In particular, model and ab initio simulations of quantum transport and optical response in molecular junctions illustrate the convenience and importance of the methodology. Results of ab initio simulations are compared with experimental data. © 2014 American Chemical Society.