skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Intermediate polaronic charge transport in organic crystals from a many-body first-principles approach
Abstract Charge transport in organic molecular crystals (OMCs) is conventionally categorized into two limiting regimes − band transport, characterized by weak electron-phonon (e-ph) interactions, and charge hopping due to localized polarons formed by strong e-ph interactions. However, between these two limiting cases there is a less well understood intermediate regime where polarons are present but transport does not occur via hopping. Here we show a many-body first-principles approach that can accurately predict the carrier mobility in this intermediate regime and shed light on its microscopic origin. Our approach combines a finite-temperature cumulant method to describe strong e-ph interactions with Green-Kubo transport calculations. We apply this parameter-free framework to naphthalene crystal, demonstrating electron mobility predictions within a factor of 1.5−2 of experiment between 100 and 300 K. Our analysis reveals the formation of a broad polaron satellite peak in the electron spectral function and the failure of the Boltzmann equation in the intermediate regime.  more » « less
Award ID(s):
1750613
PAR ID:
10316748
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
npj Computational Materials
Volume:
8
Issue:
1
ISSN:
2057-3960
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Journal of Materials Chemistry A)
    Transition metal oxides such as BiVO 4 are promising photoelectrode materials for solar-to-fuel conversion applications. However, their performance is limited by the low carrier mobility (especially electron mobility) due to the formation of small polarons. Recent experimental studies have shown improved carrier mobility and conductivity by atomic doping; however the underlying mechanism is not understood. A fundamental atomistic-level understanding of the effects on small polaron transport is critical to future material design with high conductivity. We studied the small polaron hopping mobility in pristine and doped BiVO 4 by combining Landau–Zener theory and kinetic Monte Carlo (kMC) simulation fully from first-principles, and investigated the effect of dopant–polaron interactions on the mobility. We found that polarons are spontaneously formed at V in both pristine and Mo/W doped BiVO 4 , which can only be described correctly by density functional theory (DFT) with the Hubbard correction (DFT+U) or hybrid exchange-correlation functional but not local or semi-local functionals. We found that DFT+U and dielectric dependant hybrid (DDH) functionals give similar electron hopping barriers, which are also similar between the room temperature monoclinic phase and the tetragonal phase. The calculated electron mobility agrees well with experimental values, which is around 10 −4 cm 2 V −1 s −1 . We found that the electron polaron transport in BiVO 4 is neither fully adiabatic nor nonadiabatic, and the first and second nearest neighbor hoppings have significantly different electronic couplings between two hopping centers that lead to different adiabaticity and prefactors in the charge transfer rate, although they have similar hopping barriers. Without considering the detailed adiabaticity through Landau–Zener theory, one may get qualitatively wrong carrier mobility. We further computed polaron mobility in the presence of different dopants and showed that Cr substitution of V is an electron trap while Mo and W are “repulsive” centers, mainly due to the minimization of local lattice expansion by dopants and electron polarons. The dopants with “repulsive” interactions to polarons are promising for mobility improvement due to larger wavefunction overlap and delocalization of locally concentrated polarons. 
    more » « less
  2. (, Journal of Physics: Condensed Matter)
    Abstract In the present work we theoretically analyze thermoelectric transport in single-molecule junctions (SMJ) characterized by strong interactions between electrons on the molecular linkers and phonons in their nuclear environments where electron hopping between the electrodes and the molecular bridge states predominates in the steady state electron transport. The analysis is based on the modified Marcus theory accounting for the lifetime broadening of the bridge’s energy levels. We show that the reorganization processes in the environment accompanying electron transport may significantly affect SMJ thermoelectric properties both within and beyond linear transport regime. Specifically, we study the effect of environmental phonons on the electron conductance, the thermopower and charge current induced by the temperature gradient applied across the system. 
    more » « less
  3. ; ; ; ; (, Physical Review X)
    First-principles calculations of electron interactions in materials have seen rapid progress in recent years, with electron-phonon (e-ph) interactions being a prime example. However, these techniques use large matrices encoding the interactions on dense momentum grids, which reduces computational efficiency and obscures interpretability. For e-ph interactions, existing interpolation techniques leverage locality in real space, but the high dimensionality of the data remains a bottleneck to balance cost and accuracy. Here we show an efficient way to compress e-ph interactions based on singular value decomposition (SVD), a widely used matrix and image compression technique. Leveraging (un)constrained SVD methods, we accurately predict material properties related to e-ph interactions—including charge mobility, spin relaxation times, band renormalization, and superconducting critical temperature—while using only a small fraction (1%–2%) of the interaction data. These findings unveil the hidden low-dimensional nature of e-ph interactions. Furthermore, they accelerate state-of-the-art first-principles e-ph calculations by about 2 orders of magnitude without sacrificing accuracy. Our Pareto-optimal parametrization of e-ph interactions can be readily generalized to electron-electron and electron-defect interactions, as well as to other couplings, advancing quantitative studies of condensed matter. 
    more » « less
  4. ; ; ; ; ; (, Physical Review Research)
    Understanding electronic interactions in high-temperature superconductors is an outstanding challenge. In the widely studied cuprate materials, experimental evidence points to strong electron-phonon ( e -ph) coupling and broad photoemission spectra. Yet, the microscopic origin of this behavior is not fully understood. Here, we study e -ph interactions and polarons in a prototypical parent (undoped) cuprate, La 2 CuO 4 (LCO), by means of first-principles calculations. Leveraging parameter-free Hubbard-corrected density functional theory, we obtain a ground state with the band gap and Cu magnetic moment in nearly exact agreement with experiments. This enables a quantitative characterization of e -ph interactions. Our calculations reveal two classes of longitudinal optical (LO) phonons with strong e -ph coupling to hole states. These modes consist of bond stretching and bond bending in the Cu-O plane as well as vibrations of apical O atoms. The hole spectral functions, obtained with a cumulant method that can capture strong e -ph coupling, exhibit broad quasiparticle peaks with a small spectral weight ( Z ≈ 0.25 ) and pronounced LO-phonon sidebands characteristic of polaron effects. Our calculations predict features observed in photoemission spectra, including a 40-meV peak in the e -ph coupling distribution function not explained by existing models. These results show that the universal strong e -ph coupling found experimentally in doped lanthanum cuprates is also present in the parent compound, and elucidate its microscopic origin. 
    more » « less
  5. ; ; (, Physical Review B)
    Electron-phonon (e-ph) interactions arise in many strongly correlated quantum materials from the modulation of the nearest-neighbor hopping integrals, as in the celebrated Su-Schrieffer-Heeger (SSH) model. Nevertheless, relatively few non-perturbative studies of correlated SSH models have been conducted in dimensions greater than one, and those that have been done have primarily focused on bond models, where generalized displacements independently modulate each hopping integral. We conducted a sign-problem free determinant quantum Monte Carlo study of the optical SSH-Hubbard model on a two-dimensional square lattice, where site-centered phonon modes simultaneously modulate pairs of nearest-neighbor hopping integrals. We report the model’s low-temperature phase diagram in the challenging adiabatic regime ($\Omega/E_F \sim 1/8). It exhibits insulating antiferromagnetic Mott and bond-order-wave (BOW) phases with a narrow region of coexistence between them. We also find that a critical e-ph coupling is required to stabilize the BOW phase in the small U limit. Lastly, in stark contrast to recent findings for the model’s bond variant, we find no evidence for a long-range antiferromagnetism in the pure (U/t = 0) optical SSH model. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email