Reliable Computational Prediction of the Supramolecular Ordering of Complex Molecules under Electrochemical Conditions

Abstract

We propose a computationally lean, two-stage approach that reliably predicts self-assembly behavior of complex charged molecules on metallic surfaces under electrochemical conditions. Stage one uses ab initio simulations to provide reference data for the energies (evaluated for archetypical configurations) to fit the parameters of a conceptually much simpler and computationally less expensive force field of the molecules: classical, spherical particles, representing the respective atomic entities; a flat and perfectly conducting wall represents the metallic surface. Stage two feeds the energies that emerge from this force field into highly efficient and reliable optimization techniques to identify via energy minimization the ordered ground-state configurations of the molecules. We demonstrate the power of our approach by successfully reproducing, on a semiquantitative level, the intricate supramolecular ordering observed experimentally for PQP + and ClO 4 – molecules at an Au(111)–electrolyte interface, including the formation of open-porous, self-host–guest, and stratified bilayer phases as a function of the electric field at the solid–liquid interface. We also discuss the role of the perchlorate ions in the self-assembly process, whose positions could not be identified in the related experimental investigations.

Effective screening of medium-assisted Van der Waals interactions between embedded particles

“…Nevertheless, the simple form of our result is useful for adjusting Van der Waals corrections of molecules within implicit solvents [31]. Furthermore, the screening might affect also molecular dynamics calculations in aqueous environment such as the important problem of protein folding [51], or may resolve some of the discrepancies between simulated and experimental dielectric constants [52].…”

“…with an averaged main-frequency ω [Eqs. (15) and (31)]. In general the screening coefficient can be evaluated from the dielectric function ε(ω) by using the Kramers-Kronig relation [38,39,13]…”

“…While appropriate in case that both interacting particles are within the same cavity [30] this approach disregards screening by an implicit environment. It was therefore suggested to scale the van der Waals contributions by ε −2 (ω) with ω in the optical range [31].…”

Disordered Two-Dimensional Self-Organization of Ethyl Pyruvate Molecules on the Pt(111) Surface

“…Tools like evolutionary algorithms (EA) are well established in chemistry, for example, for global cluster structure optimization in vacuo, 30 in solvents 31,32 and on surfaces, 33,34 and also for different aims like abstract point charges for catalysis by optimized external electric fields. 35,36 EAs have also been applied to simplified models of molecular interaction on surfaces, for example, to study complex, charged molecules under electrochemical conditions, by system-specific, simple force fields, 37 or to optimize graph representations for NO on Pt 2 Sn(111) and for propyne on a PdIn(021) step surface. 38 However, as we 33,34 and others 39 directly, without strong a priori model assumptions on intermolecular interactions.…”

“…EAs have also been applied to simplified models of molecular interaction on surfaces, for example, to study complex, charged molecules under electrochemical conditions, by system-specific, simple force fields, or to optimize graph representations for NO on Pt 2 Sn­(111) and for propyne on a PdIn(021) step surface . However, as we , and others have shown, it is also possible and useful to apply EA methods to such systems directly, without strong a priori model assumptions on intermolecular interactions.…”