Over the past few decades, quantum chemical molecular electronic response property calculations have gone from being state-of-the-art sophisticated work to routine keyword-driven applications of standard software—today they often represent the needed core in more complicated models of real systems which include intra- and inter-molecular interactions as well as nuclear motions. Our contribution to the continued development of this field is predominantly concerned with the treatment of heavy elements with important spin-orbit interactions as well as the treatment of electronic resonances in absorption spectroscopies.
By combining molecular dynamics and response theory, we can determine optical response properties of conformationally flexible conjugated chromophores in liquid or solid state phases. The illustrated chromophore is a dendrimer capped platinum(II) ethynyl derivative that is used in applications of optical limiting.
J. Phys. Chem. A, 2010, 114, 4981
With the introduction of damping terms in the electronic equations-of-motions, it is possible to take into account other molecular decay processes than stimulated emission in wave function response theory. In the presence of external electro-magnetic fields of modest intensity, the excited state populations may, under such conditions, remain small even under resonance conditions, and the equations-of-motions can be solved by means of perturbation theory, giving rise to linear and nonlinear response functions (or polarization propagators) that determine the time-dependence of the polarization. The main characteristic of response functions associated with resonant external fields (as compared to the nonresonant situation) is the fact that they become complex-valued (instead of real-valued) with real and imaginary parts that are related by the Kramers–Kronig relation and associated with different spectroscopies.
From the imaginary part of the linear response function for electric-dipole operators, i.e., the polarizability, we determine the linear absorption cross section. The complex polarization propagator approach offers, in this manner, a universal description of absorption spectroscopy in the visible, ultra-violet, and X-ray regions. We use this technique to help interpret near-edge X-ray absorption fine structure spectra of self-assembled monolayer samples of conjugated biochemical receptor molecules.
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Last updated: 01/20/11