Abstract
We present a fully analytic approach to calculate infrared (IR) and Raman spectra of molecules embedded in complex molecular environments modeled using the fragment-based polarizable embedding (PE) model. We provide the theory for the calculation of analytic second-order geometric derivatives of molecular energies and first-order geometric derivatives of electric dipole moments and dipole–dipole polarizabilities within the PE model. The derivatives are implemented using a general open-ended response theory framework, thus allowing for an extension to higher-order derivatives. The embedding-potential parameters used to describe the environment in the PE model are derived through first-principles calculations, thus allowing a wide variety of systems to be modeled, including solvents, proteins, and other large and complex molecular environments. Here, we present proof-of-principle calculations of IR and Raman spectra of acetone in different solvents. This work is an important step toward calculating accurate vibrational spectra of molecules embedded in realistic environments.
Highlights
Vibrational spectroscopy, in particular infrared (IR) absorption and Raman scattering, is one of the most important spectroscopic methods for elucidating molecular structure.[1]
Our focus in the discussion is on the inclusion of the effect of different solvents through the polarizable embedding (PE) model and polarizable continuum model (PCM)
It is worth noting that the spectra for acetone in chloroform and acetone solutions are virtually overlapping, suggesting no significant differences in the solute−solvent structure and dynamics for these two solvents
Summary
Vibrational spectroscopy, in particular infrared (IR) absorption and Raman scattering, is one of the most important spectroscopic methods for elucidating molecular structure.[1]. On the other hand, are found from the normal-mode displacement gradient of the relevant polarization properties, which for IR absorption is the electric dipole moment and for Raman scattering is the electric dipole−dipole polarizability.[5] From a computational perspective, an added challenge in the calculation of vibrational properties compared to, for instance, properties involving only electric-dipole perturbations[6] is the dependence of the basis functions on the nuclear positions.[2,4] The theory and implementations of analytic first-7 and second-order[8] geometric derivatives of molecular energies were presented already in the late 1960s and 1970s, respectively.
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