Freitag, 8. Januar 2016

A summary of recent publications and their connection to equilibrium solvation - happy 2016!

Let me begin 2016 with a summary of a couple of papers that have been accepted for publication in recent weeks before I use one of them to lead over to the ongoing work I reported in the last two posts.

A few weeks ago, my wife Steffi and I celebrated our first "Mewes & Mewes et al" paper making it into PCCP. It offers a fresh perspective onto the electronic structure of excitons in poly(para-phenylene vinylene) or short PPV, which is something like the guinea pig of the organic electronics community. We studied PPV using highly accurate ab-initio quantum-chemical methods (ADC of up to third order) in combination with the very handy wavefunction analysis routines developed by Felix and Steffi.

Furthermore, two other papers to which I contributed were published recently:
  • Firstly, there is this work in PNAS on signatures and control of strong-field dynamics in a complex (i.e. molecular) system. My contribution to this work were quantum-chemical insights, which eventually helped Kristina and her co-workers to set up a theoretical model to simulate the exposure and response of molecules to strong laser pulses.
  • Secondly, we finally managed to publish the second paper on our  non-equilibrium PCM in Q-Chem. This second article is concerned with unexpected discrepancies between two alternative schemes of separating the fast and slow components of the polarization (I explained this in one of my recent posts). Zhi-Qiang found that the so-called Pekar and Marcus partitioning of the polarization, which should formally lead to identical results, yield significantly different results. In the article, he traces this back to the discretization of the PCM equations for the actual, numerical implementation. Eventually, he demonstrates that SSVPE (one of the three common flavours of PCMs besides the conductor-like approximation (C-PCM) and the integral-equation formalism (IEF-PCM)) exhibit the largest deviations (they are still rather small and in the ballpark of 0.01~eV)
Interestingly, this last finding directly relates to my current work on equilibrium solvation models. I fortuitously found very similar results for C-PCM, IEF-PCM and SSVPE while doing a little sanity test of my solvent-field equilibration code. For this purpose, I combined the perturbative non-equilibrium formalism with the new, self-consistent equilibrium solvation functionality. My expectation was that the non-equilibrium corrections for any state should become zero during the solvent-field equilibration for the respective state. Why? Because the non-equilibrium correction constitutes a perturbative estimate of how the relaxation of the fast component of the polarization with respect to a certain excited state would reduce its energy. But obviously, the energy should not be changed if the solvent field is already fully equilibrated for the respective state.
Surprisingly, the non-equilibrium terms do become zero only with C-PCM and IEF-PCM, but not with SSVPE. The deviations I find are in the same ballpark as the differences between the Pekar and Marcus schemes. Currently, I'm in the process of writing up these results and hence, expect more updates the in near future.

So long!