Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 117, Issue 19, Pages 10142-10148Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1921273117
Keywords
quasi-Fermi level splitting; first-principles calculations; nonequilibrium quantum transport; voltage drops; single-molecule junctions
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Funding
- Nano-Material Technology Development Program of the National Research Foundation - Ministry of Science and ICT (Information and Communication Technology) of Korea [2016M3A7B4024133]
- Basic Research Program of the National Research Foundation - Ministry of Science and ICT (Information and Communication Technology) of Korea [2017R1A2B3009872]
- Global Frontier Program of the National Research Foundation - Ministry of Science and ICT (Information and Communication Technology) of Korea [2013M3A6B1078882]
- Basic Research Lab Program of the National Research Foundation - Ministry of Science and ICT (Information and Communication Technology) of Korea [2020R1A4A2002806]
- Korea Institute of Science and Technology Information Supercomputing Center [KSC-2018-C2-0032]
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The splitting of quasi-Fermi levels (QFLs) represents a key concept utilized to describe finite-bias operations of semiconductor devices, but its atomic-scale characterization remains a significant challenge. Herein, the nonequilibrium QFL or electrochemical potential profiles within single-molecule junctions obtained from the first-principles multispace constrained-search density-functional formalism are presented. Benchmarking the standard nonequilibrium Green's function calculation results, it is first established that algorithmically the notion of separate electrode-originated nonlocal QFLs should be maintained within the channel region during self-consistent finite-bias electronic structure calculations. For the insulating hexandithiolate junction, the QFL profiles exhibit discontinuities at the left and right electrode interfaces and across the molecule the accompanying electrostatic potential drops linearly and Landauer residual-resistivity dipoles are uniformly distributed. For the conducting hexatrienedithiolate junction, on the other hand, the electrode QFLs penetrate into the channel region and produce split QFLs. With the highest occupied molecular orbital entering the bias window and becoming a good transport channel, the split QFLs are accompanied by the nonlinear electrostatic potential drop and asymmetric Landauer residual-resistivity dipole formation. Our findings underscore the importance of the first-principles extraction of QFLs in nanoscale junctions and point to a future direction for the computational design of nextgeneration semiconductor devices.
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