arXiv subjects

Yenni P. Ortiz

Publications and source records attributed to Yenni P. Ortiz.

7 recordsLinked to original sources

arXiv2025

Electric-Field-Induced Tautomerism in Metal-Free Benziporphyrins Enables Aromaticity-Controlled Conductance Switching

Metal-free porphyrins can switch between hydrogen-bonded tautomers, potentially enabling reversible control in molecular electronics. However, electric field gating of porphyrin tautomerism, which is critical for device integration, has not been fully realized. We propose metal-free benziporphyrins (MFBPs), in which one pyrrole ring is replaced with a phenol group, as a new platform for tautomer-based molecular electronics. This approach introduces asymmetry, which allows for three distinct tautomers, each possessing a characteristic aromatic or antiaromatic electronic structure. Density functional theory and quantum transport calculations show that: i) experimentally realisable electric fields can selectively stabilize each tautomer, and ii) each tautomer exhibits a characteristic conductance profile. The strong switching capability of MFBPs is demonstrated by ON/OFF ratios exceeding 500 at low bias. Fused MFBPs further expand functionality by providing multiple tautomeric states for multistate molecular registers and enabling wire-like architectures with enhanced conductance. These results establish MFBPs as versatile building blocks for electric-field-responsive molecular devices and open new research opportunities for molecular-scale logic and memory.

physics.chem-ph↗

arXiv2025

Lithium Adsorbtion on Polyacenes $\&$ Zig-zag-edge Graphene Strips

The effect of increased electron-density (from adsorbed Li atoms) in polyacenes and in nano-ribbons with zig-zag edge is discussed in terms of resonance theoretical considerations and in terms edge-localized frontier molecular orbitals. The argumentation from simple pictures is finally using the density functional theory (DFT) for anthracene, polyacene polymer and graphene strips. Some discussion is made for zig-zag edge graphene.

physics.chem-ph↗

arXiv2020

Current vortices in aromatic carbon molecules

The local current flow through three small aromatic carbon molecules, namely benzene, naphthalene and anthracene, is studied. Applying density functional theory and the non-equilibrium Green's function method for transport, we demonstrate that pronounced current vortices exist at certain electron energies for these molecules. The intensity of these circular currents, which appear not only at the anti-resonances of the transmission but also in vicinity of its maxima, can exceed the total current flowing through the molecular junction and generate considerable magnetic fields. The $π$ electron system of the molecular junctions is emulated experimentally by a network of macroscopic microwave resonators. The local current flows in these experiments confirm the existence of current vortices as a robust property of ring structures. The circular currents can be understood in terms of a simple nearest-neighbor tight-binding Hückel model. Current vortices are caused by the interplay of the complex eigenstates of the open system which have energies close-by the considered electron energy. Degeneracies, as observed in benzene and anthracene, can thus generate strong circular currents, but also non-degenerate systems like naphthalene exhibit current vortices. Small imperfections and perturbations can couple otherwise uncoupled states and induce circular currents.

cond-mat.mes-hall↗

arXiv2017

Chains of benzenes with lithium-atom adsorption: Vibrations and spontaneous symmetry breaking

We study effects of different configurations of adsorbates on the vibrational modes as well as symmetries of polyacenes and poly-p-phenylenes focusing on lithium atom adsorption. We found that the spectra of the vibrational modes distinguish the different configurations. For more regular adsorption schemes the lowest states are bending and torsion modes of the skeleton, which are essentially followed by the adsorbate. On poly-p-phenylenes we found that lithium adsorption reduces and often eliminates the torsion between rings thus increasing symmetry. There is spontaneous symmetry breaking in poly-p-phenylenes due to double adsorption of lithium atoms on alternating rings.

physics.chem-ph↗

arXiv2016

Microwave emulations and tight-binding calculations of transport in polyacetylene

A novel approach to investigate the electron transport of cis- and trans-polyacetylene chains in the single-electron approximation is presented by using microwave emulation measurements and tight-binding calculations. In the emulation we take into account the different electronic couplings due to the double bonds leading to coupled dimer chains. The relative coupling constants are adjusted by DFT calculations. For sufficiently long chains a transport band gap is observed if the double bonds are present, whereas for identical couplings no band gap opens. The band gap can be observed also in relatively short chains, if additional edge atoms are absent, which cause strong resonance peaks within the band gap. The experimental results are in agreement with our tight-binding calculations using the nonequilibrium Green's function method. The tight-binding calculations show that it is crucial to include third nearest neighbor couplings to obtain the gap in the cis-polyacetylene.

cond-mat.mes-hall↗

arXiv2015

Energies for cyclic and acyclic aggregations of adamantane and diamantane units sharing vertices, edges, or six-membered rings

Diamondoids are hydrocarbons having a carbon scaffold comprised from polymer-like composites of adamantane cages. The present paper describes computed total energies and "SWB-tension" energies (often referred to as "strain" energies) for species having $n$ adamantane or diamantane units sharing pairwise: one carbon atom (spiro-[n]adamantane or spiro-[$n$]diamantane); one C-C bond (one-bond-sharing-[$n$]adamantane or one-bond-sharing-[$n$]diamantane); or one chair-shaped hexagon of carbon atoms (1234-helical-cata-[$n$]diamantanes). Each of the five investigated polymer-like types is considered either as an acyclic or a cyclic chain of adamantane- or diamantane-unit cages. With increasing $n$ values, SWB-tension energies for acyclic aggregates are found to increase linearly, while the net SWB-tension energies of cyclic aggregates often go thru a minimum at a suitable value of $n$. In all five cases, a limiting common energy per unit ($E/n$ ) is found to be approached by both cyclic and acyclic chains as $n\to \infty $, as revealed from plots of $E/n$ versus $1/n$ for acyclic chains and of $E/n$ versus $1/n^2$ for cyclic chains.

physics.chem-ph↗

arXiv2010

Spontaneous symmetry breaking by double lithium adsorption in polyacenes

We show that adsorption of one lithium atom to a polyacenes, i.e. chains of linearly fused benzene rings, will cause this chain to be slightly deformed. If we adsorb a second identical atom on the opposite side of the same ring, this deformation is dramatically enhanced despite of the fact, that a symmetric configuration seems possible. We argue, that this may be due to an instability of the Jahn-Teller type possibly indeed to a Peierls instability.

physics.chem-ph↗