Predicting dipole orientations in spontelectric methyl formate

Abstract

Capturing intermolecular interactions accurately is essential for describing, e.g., morphology of molecular matter on the nanoscale. When it reveals characteristics which are not directly accessible through experiments or ab initio theories, a model here becomes eminently beneficial. In laboratory astrochemistry, the intense study of ices has led i.a. to the exploration of the spontelectric state of nanofilms. Despite its success in biophysics or biochemistry and despite its predictive power, molecular modeling has however not yet been widely deployed for solid-state astrochemistry. In this article, therefore a pertinent hitherto unaddressed problem is tackled by means of the classical molecular-dynamics method, namely the unknown distribution of relative dipole orientations in spontelectric cis-methyl formate (MF). In doing so, from ab initio data, a molecular model is derived which confirms for the first time the anomalous temperature-dependent polarization of MF. These insights thus represent a further step toward understanding spontelectric behavior. Moreover, unprecedented first-principles predictions are reported regarding the ground-state geometry of the MF trimer and tetramer. In conjunction with the study of the binding to carbonaceous substrates, these additional findings can help to exemplarily elucidate molecular ice formation in astrochemical settings. Graphic Abstract

A theoretical study on spontaneous dipole orientation in ice structures

“…The present work represents the first molecular dynamics study of deposition resulting in a spontelectric material. ‡ We however note that Kexel and Solov'yov 11 have done simulations of spontelectric field in cis-methyl formate structures.…”

“…The present work represents the first molecular dynamics study of deposition resulting in a spontelectric material ‡‡In the standard model of spontelectrics, the field is constant in the film with respect to the height above the substrate 1 , while in our case it varies somewhat in magnitude but we still refer to this as a spontelectric effect. We however note that Kexel and Solov’yov 11 have done simulations of spontelectric field in cis -methyl formate structures.…”

A Spontaneously Electrical State of Matter

“…In earlier work, we made a qualitative suggestion that librational fluctuations were an underlying cause of the spontelectric effect, as supported by recent large scale simulations of cis-methyl formate films. 52 Strikingly, the molecular dynamics simulations in 52, based on ab initio potentials, reproduced the variation in net orientation in cismethyl formate versus temperature of deposition, giving a value of deposition temperature for the minimum of around 70 K, close to that observed at 77.5 K.…”