First-principles study on photoswitching behavior and negative differential resistance in single molecule junction

Theoretical study on the structure, spectroscopic, and current-voltage behavior of 11-Cis and Trans retinal isomers in rhodopsin

In this study, the electronic transport properties of 11-Cis and Trans retinal, components of rhodopsin, were investigated as optical molecular switches using the nonequilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT). These isomers, which can be reversibly converted into each other, were examined in detail. The structural and spectroscopic properties, including infrared (IR), Raman, nuclear magnetic resonance (NMR), and ultraviolet (UV) spectra, were analyzed using the hybrid B3LYP/6-311 +  + G** level of theory. Complete vibrational assignments were performed for both forms utilizing the scaled quantum mechanical force field (SQMFF) methodology. To evaluate the conductivity of these molecules, we utilized current-voltage (I-V) characteristics, transmission spectra, molecular projected self-consistent Hamiltonian (MPSH), HOMO-LUMO gap, and second-order interaction energies (E2). The trendline extrapolation of the current-voltage plots confirmed our findings. We investigated the effect of different electrodes (Ag, Au, Pt) and various connection sites (hollow, top, bridge) on conductivity. The Ag electrode with the hollow site exhibited the highest efficiency. Our results indicate that the Cis form has higher conductivity than the Trans form.

Water-accelerated π-Stacking Reaction in Benzene Cluster Cation

Single molecule electron devices (SMEDs) have been widely studied through both experiments and theoretical calculations because they exhibit certain specific properties that general macromolecules do not possess. In actual SMED systems, a residual water molecule strongly affects the electronic properties of the SMED, even if only one water molecule is present. However, information about the effect of H₂O molecules on the electronic properties of SMEDs is quite limited. In the present study, the effect of H₂O on the ON-OFF switching property of benzene-based molecular devices was investigated by means of a direct ab initio molecular dynamics (AIMD) method. T- and H-shaped benzene dimers and trimers were examined as molecular devices. The present calculations showed that a H₂O molecule accelerates the π-stacking formation in benzene molecular electronic systems. The times of stacking formation in a benzene dimer cation (n = 2) were calculated to be 460 fs (H₂O) and 947 fs (no-H₂O), while those in a trimer cation (n = 3) were 551 fs (H₂O) and 1019 fs (no-H₂O) as an average of the reaction time. This tendency was not dependent on the levels of theory used. Thus, H₂O produced positive effects in benzene-based molecular electronics. The mechanism of π-stacking was discussed based on the theoretical results.

Influence of spatial distribution of molecule on the switching behavior: A first-principles study

We perform first-principles calculations to investigate the electronic transport properties of chalcone and flavanone molecules sandwiched between graphene electrodes. These two molecules can be reversibly converted between open and closed states induced by pH, and the significant switching behaviors are observed. The currents and switching ratios are influenced by rotating molecules around the [Formula: see text] axis, which are discussed by the transmission eigenstates, electrostatic potential distributions and transmission spectra. The observed negative differential resistance effect is explained in chalcone configuration. The results suggest that spatial distributions of molecules will influence the performance of devices, indicating a potential application in future molecular circuits.