An official website of the United States government
We employ deep kernel learning electronic coarse-graining (DKL-ECG) with approximate Gaussian processes as a flexible and scalable framework for learning heteroscedastic electronic property distributions as a smooth function of coarse-grained (CG) configuration. The appropriateness of the Gaussian prior on predictive CG property distributions is justified as a function of CG model resolution by examining the statistics of target distributions. The certainties of predictive CG distributions are shown to be limited by CG model resolution with DKL-ECG predictive noise converging to the intrinsic physical noise induced by the CG mapping operator for multiple chemistries. Further analysis of the resolution dependence of learned CG property distributions allows for the identification of CG mapping operators that capture CG degrees of freedom with strong electron–phonon coupling. We further demonstrate the ability to construct the exact quantum chemical valence electronic density of states (EDOS), including behavior in the tails of the EDOS, from an entirely CG model by combining iterative Boltzmann inversion and DKL-ECG. DKL-ECG provides a means of learning CG distributions of all-atom properties that are traditionally “lost” in CG model development, introducing a promising methodological alternative to backmapping algorithms commonly employed to recover all-atom property distributions from CG simulations.
more »
« less
Accessing the electronic structure of liquid crystalline semiconductors with bottom-up electronic coarse-graining
Understanding the relationship between multiscale morphology and electronic structure is a grand challenge for semiconducting soft materials. Computational studies aimed at characterizing these multiscale relationships require the complex integration of quantum-chemical (QC) calculations, all-atom and coarse-grained (CG) molecular dynamics simulations, and back-mapping approaches. However, the integration and scalability of these methods pose substantial computational challenges that limit their application to the requisite length scales of soft material morphologies. Here, we demonstrate the bottom-up electronic coarse-graining (ECG) of morphology-dependent electronic structure in the liquid-crystal-forming semiconductor, 2-(4-methoxyphenyl)-7-octyl-benzothienobenzothiophene (BTBT). ECG is applied to construct density functional theory (DFT)-accurate valence band Hamiltonians of the isotropic and smectic liquid crystal (LC) phases using only the CG representation of BTBT. By bypassing the atomistic resolution and its prohibitive computational costs, ECG enables the first calculations of the morphology dependence of the electronic structure of charge carriers across LC phases at the ~20 nm length scale, with robust statistical sampling. kinetic Monte Carlo (kMC) simulations reveal a strong morphology dependence on zero-field charge mobility among different LC phases as well as the presence of two-molecule charge carriers that act as traps and hinder charge transport. We leverage these results to further evaluate the feasibility of developing truly mesoscopic, field-based ECG models in future works. The fully CG approach to electronic property predictions in LC semiconductors opens a new computational direction for designing electronic processes in soft materials at their characteristic length scales.
more »
« less
- Award ID(s):
- 2154916
- PAR ID:
- 10574844
- Publisher / Repository:
- Royal Society of Chemistry (RSC)
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 15
- Issue:
- 22
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 8390 to 8403
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)The electronic, vibrational, and charge-transport properties of a series of benzothieno-benzothiophene (BTBT)–F m TCNQ ( m = 0, 2, 4) and diC n BTBT–F m TCNQ ( n = 8, 12; m = 0, 4) donor–acceptor (DA) co-crystals have been investigated by means of density functional theory calculations. The electronic-structure calculations predict wide conduction bands and small effective masses for electrons along the DA stacking directions. The results indicate that the increase in the number of F atoms on the acceptor molecules results in an increase of superexchange couplings along the DA stacks, while the addition of the alkyl side chains results in a decrease of through-space transfer integrals between neighboring stacks. Time-dependent density functional theory calculations of the optical properties describe the lowest two optical transitions as having a charge-transfer character and being related to the two electronic coupling pathways that contribute to the superexchange couplings. The results also indicate that the ionicity parameter in the diC n BTBT–F m TCNQ cocrystals is somewhat larger than in the BTBT analogues. Overall, we find that DFT calculations based on periodic boundary conditions are a reliable tool to estimate the ionicity parameter in DA cocrystals.more » « less
-
null (Ed.)Computational methods can provide first-principles insights into the thermochemistry and kinetics of reactions at interfaces, but this capability has not been widely leveraged to design soft materials that respond selectively to chemical species. Here we address this opportunity by demonstrating the design of micrometer-thick liquid crystalline films supported on metal-perchlorate surfaces that exhibit selective orientational responses to targeted oxidizing gases. Initial electronic structure calculations predicted Mn 2+ , Co 2+ , and Ni 2+ to be promising candidate surface binding sites that (1) coordinate with nitrile-containing mesogens to orient liquid crystal (LC) phases and (2) undergo redox-triggered reactions upon exposure to humid O 3 leading to a change in the strength of binding of the nitrile group to the surface. These initial predictions were validated by experimental observations of orientational transitions of nitrile-containing LCs upon exposure to air containing parts-per-billion concentrations of O 3 . Additional first-principles calculations of reaction free energies of metal salts and oxidizing gases predicted that the same set of metal cations, if patterned on surfaces at distinct spatial locations, would provide LC responses that allow Cl 2 and O 3 to be distinguished while not responding to environmental oxidants such as O 2 and NO 2 . Experimental results are provided to support this prediction, and X-ray diffraction measurements confirmed that the experimentally observed LC responses can be understood in terms of the relative thermodynamic driving force for formation of MnO 2 , CoOOH, or NiOOH from the corresponding metal cation binding sites in the presence of humid O 3 and Cl 2 .more » « less
-
Abstract By eliminating unnecessary details, coarse-grained (CG) models provide the necessary efficiency for simulating scales that are inaccessible to higher resolution models. However, because they average over atomic details, the effective potentials governing CG degrees of freedom necessarily incorporate significant entropic contributions, which limit their transferability and complicate the treatment of thermodynamic properties. This work employs a dual-potential approach to consider the energetic and entropic contributions to effective interaction potentials for CG models. Specifically, we consider one- and three-site CG models for ortho-terphenyl (OTP) both above and below its glass transition. We employ the multiscale coarse-graining (MS-CG) variational principle to determine interaction potentials that accurately reproduce the structural properties of an all-atom (AA) model for OTP at each state point. We employ an energy-matching variational principle to determine an energy operator that accurately reproduces the intra- and inter-molecular energy of the AA model. While the MS-CG pair potentials are almost purely repulsive, the corresponding pair energy functions feature a pronounced minima that corresponds to contacting benzene rings. These energetic functions then determine an estimate for the entropic component of the MS-CG interaction potentials. These entropic functions accurately predict the MS-CG pair potentials across a wide range of liquid state points at constant density. Moreover, the entropic functions also predict pair potentials that quite accurately model the AA pair structure below the glass transition. Thus, the dual-potential approach appears a promising approach for modeling AA energetics, as well as for predicting the temperature-dependence of CG effective potentials.more » « less
-
Recent coarse-grained (CG) models have often supplemented conventional pair potentials with potentials that depend upon the local density around each particle. In this work, we investigate the temperature-dependence of these local density (LD) potentials. Specifically, we employ the multiscale coarse-graining (MS-CG) force-matching variational principle to parameterize pair and LD potentials for one-site CG models of molecular liquids at ambient pressure. The accuracy of these MS-CG LD potentials quite sensitively depends upon the length-scale, rc, that is employed to define the local density. When the local density is defined by the optimal length-scale, rc*, the MS-CG potential often accurately describes the reference state point and can provide reasonable transferability across a rather wide range of temperatures. At ambient pressure, the optimal LD length-scale varies linearly with temperature over a very wide range of temperatures. Moreover, if one adopts this temperature-dependent LD length-scale, then the MS-CG LD potential appears independent of temperature, while the MS-CG pair potential varies linearly across this temperature range. This provides a simple means for predicting pair and LD potentials that accurately model new state points without performing additional atomistic simulations. Surprisingly, at certain state points, the predicted potentials provide greater accuracy than MS-CG potentials that were optimized for the state point.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3SC06749A
