First-Principles Approach to Elucidating Significant Rectification Ratios in Oppositely Charged Dipeptides

The electron transport properties of shorter peptides (i.e., dipeptides) consisting of oppositely charged amino acids have paved the way for the design of miniaturized molecular devices. In this context, we investigated two different dipeptides, namely arginyl-aspartic and arginyl-glutamic, alternating between one positively charged (i.e., l -arginine) and two negatively charged (i.e., l -aspartic and l -glutamic) amino acids. These dipeptides are placed between Au, Ag and Cu electrodes to form a total of six individual molecular devices. Various transport parameters including conductance, HOMO-LUMO gap, dipole moment, current–voltage (I–V) characteristics, rectification ratio and negative differential resistance regimes are computed using density functional theory with non-equilibrium Green’s function (NEGF-DFT). We observe an exceptionally high rectification ratio of 197.2 with the Au-Arg-Asp-Au device, while the Au-Arg-Glu-Au device offers the most significant negative differential resistance (NDR) regime, with a peak-to-valley current ratio of 178.9. We focus on the standard electron exchange–correlation integration of the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA) with the double-zeta double-polarized (DZDP) basis set. The conductance, transmission spectra, delocalization of significant frontier orbitals and their gap correlate well with the switching characteristics. The coupling between molecule and electrode predicts the range of I–V characteristics. These results reveal the significant role of dipeptides in future molecular electronic devices. Graphical Abstract