Next‐generation QTAIM for scoring molecular wires in E‐fields for molecular electronic devices

• Published in: Journal of computational chemistry 2020-04, Vol.41 (9), p.913-921
• Main Authors: Azizi, Alireza, Momen, Roya, Früchtl, Herbert, Mourik, Tanja, Kirk, Steven R., Jenkins, Samantha
• Format: Article
• Language: English
• Subjects: Chemical bonds; Critical point; Electric fields; Electronic devices; Ellipticity; Ethylene; Hydrogen bonds; Polarization; Quantum theory
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.26137

The effect of a varying, directional E x, E y, and E z electric field on the ethene molecule was investigated using next‐generation quantum theory of atoms in molecules (QTAIM). Despite using low E‐field strengths that are within the realm of experiment and do not measurably alter the molecular geometry, significant changes to the QTAIM properties were observed. Using conventional QTAIM, the shifting of the C─C and C─H bond critical points (BCPs) demonstrates polarization through an interchange in the size of the atoms involved in a bond, since a BCP is located on the boundary between a pair of bonded atoms. Next‐generation QTAIM, however, demonstrates the polarization effect more directly with a change in morphology of the 3‐D envelope around the BCP. Modest increases of ≈ 2% in the ellipticity ε of the BCP were uncovered when the C─C bond was aligned parallel or anti‐parallel to the applied E x‐field. Significant asymmetries were found in the response of the next‐generation QTAIM 3‐D paths of the C─H bonds to the applied E‐field. When the E‐field coincided with the C─C bond, the BCP moved in response and was accompanied by the envelope constructed from 3‐D next‐generation paths. The response displayed a polarization effect that increased with increasing magnitude of the E x‐field parallel and anti‐parallel to the C─C bond. Our analysis demonstrates that next‐generation QTAIM is a useful tool for understanding the response of molecules to E‐fields, for example, for the screening of molecular wires for the design of molecular electronic devices. © 2019 Wiley Periodicals, Inc. The variation of the relative energy ΔE for values of the external E‐field up to [200 × 10−5 a.u. (60.91 kJ/mol)] where E x, E y, and E z correspond to the directions x, y, z. The E‐field direction +E x is parallel to the C1 → C2 bond direction. Insets: The {q,q'} path‐packets indicating the most preferred directions of electronic charge density motion for values of E x = −200 × 10−5 a.u. (pale‐magenta), E x = 0 (red), E x = +200 × 10−5 a.u. (dark‐magenta).