Publications
@article{RN19,
author = {Lee, Woo Seok and Cho, Yeongsu and Paritmongkol, Watcharaphol and Sakurada, Tomoaki and Ha, Seung Kyun and Kulik, Heather J and Tisdale, William A},
title = {Mixed-Chalcogen 2D Silver Phenylchalcogenides (AgE1–x E x Ph; E= S, Se, Te)},
journal = {ACS nano},
issn = {1936-0851},
doi = {10.1021/acsnano.4c15118},
year = {2024}
}
Alloying is a powerful strategy for tuning the electronic band structure and optical properties of semiconductors. Here, we investigate the thermodynamic stability and excitonic properties of mixed-chalcogen alloys of two-dimensional (2D) hybrid organic–inorganic silver phenylchalcogenides (AgEPh; E = S, Se, Te). Using a variety of structural and optical characterization techniques, we demonstrate that the AgSePh-AgTePh system forms homogeneous alloys (AgSe1–xTexPh, 0 ≤ x ≤ 1) across all compositions, whereas the AgSPh-AgSePh and AgSPh-AgTePh systems exhibit distinct miscibility gaps. Density functional theory calculations reveal that chalcogen mixing is energetically unfavorable in all cases but comparable in magnitude to the ideal entropy of mixing at room temperature. Because AgSePh and AgTePh have the same crystal structure (which is different from AgSPh), alloying is predicted to be thermodynamically preferred over phase separation in the case of AgSePh-AgTePh, whereas phase separation is predicted to be more favorable than alloying for both the AgSPh-AgSePh and AgSPh-AgTePh systems, in agreement with experimental observations. Homogeneous AgSe1–xTexPh alloys exhibit continuously tunable excitonic absorption resonances in the ultraviolet–visible range, while the emission spectrum reveals competition between exciton delocalization (characteristic of AgSePh) and localization behavior (characteristic of AgTePh). Overall, these observations provide insight into the thermodynamics of 2D silver phenylchalcogenides and the effect of lattice composition on electron–phonon interactions in 2D hybrid organic–inorganic semiconductors.
@article{RN1,
author = {Khamlue, Rattapon and Sakurada, Tomoaki and Cho, Yeongsu and Lee, Woo Seok and Leangtanom, Pimpan and Taylor, Michael G and Naewthong, Worakit and Sripetch, Pongsakun and Na Ranong, Busayakorn and Autila, Tossawat and Rungseesumran, Thiti and Kaewkhao, Jakrapong and Sudyoadsuk, Taweesak and Kopwitthaya, Atcha and Müller, Peter and Promarak, Vinich and Kulik, Heather J and Tisdale, William A and Paritmongkol, Watcharaphol},
title = {Heterocyclic Modification Leading to Luminescent 0D Metal Organochalcogenide with Stable X-ray Scintillating Properties},
journal = {Chemistry of Materials},
volume = {36},
number = {10},
pages = {5238-5249},
issn = {0897-4756},
doi = {10.1021/acs.chemmater.4c00653},
year = {2024}
}
Metal organochalcogenides (MOCs) are an emerging class of luminescent hybrid organic–inorganic semiconductors, whose structures and properties can be tuned by organic functionalization and substitutions of their metal and chalcogen elements. Herein, we present a new design strategy by heterocyclic modification, resulting in the transformation of prototypical two-dimensional (2D) silver phenylselenide (AgSePh) to a zero-dimensional (0D) silver pyridinylselenide (AgSePy) via the formation of Ag–N bonds. At room temperature, AgSePy shows strong and broad orange photoluminescence (PL; λmax = 636 nm, full-width-at-half-maximum = 111 nm, quantum yield = 64%) with a large 259 nm Stoke’s shift and a 3.4 μs lifetime. Using steady-state and time-resolved PL spectroscopy under varying temperature and oxygen conditions, we found AgSePy to exhibit air-stable luminescence and maintain a high PL quantum yield and a single exponential PL lifetime down to 4 K. Furthermore, AgSePy shows excellent thermal stability up to ∼250 °C and chemical stability against polar, nonpolar, and aqueous solvents at pH 3–14. Density functional theory calculations further confirm the 0D electronic structure. Finally, we successfully demonstrated the performance of AgSePy as an X-ray scintillator with an estimated light yield of ∼8,000 phe/MeV and a spatial resolution down to 0.080 ± 0.005 mm. Overall, this work provides a novel tactic to modify the structures and properties of MOCs, highlighting their structural richness and structure–property relationship, and introduces their new use as X-ray scintillators, encouraging further development in radiation detection and medical imaging.
@article{RN20,
author = {Cho, Yeongsu and Kulik, Heather J},
title = {Improving gas adsorption modeling for MOFs by local calibration of Hubbard U parameters},
journal = {The Journal of Chemical Physics},
volume = {160},
number = {15},
issn = {0021-9606},
doi = {10.1063/5.0201934},
year = {2024}
}
While computational screening with density functional theory (DFT) is frequently employed for the screening of metal–organic frameworks (MOFs) for gas separation and storage, commonly applied generalized gradient approximations (GGAs) exhibit self-interaction errors, which hinder the predictions of adsorption energies. We investigate the Hubbard U parameter to augment DFT calculations for full periodic MOFs, targeting a more precise modeling of gas molecule–MOF interactions, specifically for N2, CO2, and O2. We introduce a calibration scheme for the U parameter, which is tailored for each MOF, by leveraging higher-level calculations on the secondary building unit (SBU) of the MOF. When applied to the full periodic MOF, the U parameter calibrated against hybrid HSE06 calculations of SBUs successfully reproduces hybrid-quality calculations of the adsorption energy of the periodic MOF. The mean absolute deviation of adsorption energies reduces from 0.13 eV for a standard GGA treatment to 0.06 eV with the calibrated U, demonstrating the utility of the calibration procedure when applied to the full MOF structure. Furthermore, attempting to use coupled cluster singles and doubles with perturbative triples calculations of isolated SBUs for this calibration procedure shows varying degrees of success in predicting the experimental heat of adsorption. It improves accuracy for N2 adsorption for cases of overbinding, whereas its impact on CO2 is minimal, and ambiguities in spin state assignment hinder consistent improvements of O2 adsorption. Our findings emphasize the limitations of cluster models and advocate the use of full periodic MOF systems with a calibrated U parameter, providing a more comprehensive understanding of gas adsorption in MOFs.
@article{RN18,
author = {Aleksich, Mariya and Cho, Yeongsu and Paley, Daniel W and Willson, Maggie C and Nyiera, Hawi N and Kotei, Patience A and Oklejas, Vanessa and Mittan‐Moreau, David W and Schriber, Elyse A and Christensen, Kara and Inoue, Ichiro and Owada, Shigeki and Tono, Kensuke and Sugahara, Michihiro and Inaba‐Inoue, Satomi and Vakili, Mohammad and Milne, Christopher J and DallAntonia, Fabio and Khakhulin, Dmitry and Ardana‐Lamas, Fernando and Lima, Frederico and Valerio, Joana and Han, Huijong and Gallo, Tamires and Yousef, Hazem and Turkot, Oleksii and Macias, Ivette J Bermudez and Kluyver, Thomas and Schmidt, Philipp and Gelisio, Luca and Round, Adam R and Jiang, Yifeng and Vinci, Doriana and Uemura, Yohei and Kloos, Marco and Mancuso, Adrian P and Warren, Mark and Sauter, Nicholas K and Zhao, Jing and Smidt, Tess and Kulik, Heather J and Sharifzadeh, Sahar and Brewster, Aaron S and Hohman, J Nathan},
title = {Ligand‐Mediated Quantum Yield Enhancement in 1‐D Silver Organothiolate Metal–Organic Chalcogenolates},
journal = {Advanced Functional Materials},
pages = {2414914},
issn = {1616-301X},
doi = {10.1002/adfm.202414914},
year = {2024}
}
X-ray free electron laser (XFEL) microcrystallography and synchrotron single-crystal crystallography are used to evaluate the role of organic substituent position on the optoelectronic properties of metal–organic chalcogenolates (MOChas). MOChas are crystalline 1D and 2D semiconducting hybrid materials that have varying optoelectronic properties depending on composition, topology, and structure. While MOChas have attracted much interest, small crystal sizes impede routine crystal structure determination. A series of constitutional isomers where the aryl thiol is functionalized by either methoxy or methyl ester are solved by small molecule serial femtosecond X-ray crystallography (smSFX) and single crystal rotational crystallography. While all the methoxy examples have a low quantum yield (0-1%), the methyl ester in the ortho position yields a high quantum yield of 22%. The proximity of the oxygen atoms to the silver inorganic core correlates to a considerable enhancement of quantum yield. Four crystal structures are solved at a resolution range of 0.8–1.0 Å revealing a collapse of the 2D topology for functional groups in the 2- and 3- positions, resulting in needle-like crystals. Further analysis using density functional theory (DFT) and many-body perturbation theory (MBPT) enables the exploration of complex excitonic phenomena within easily prepared material systems.
@article{RN2,
author = {Roh, Heejung and Kim, Dong‐Ha and Cho, Yeongsu and Jo, Young‐Moo and Del Alamo, Jesús A and Kulik, Heather J and Dincă, Mircea and Gumyusenge, Aristide},
title = {Robust Chemiresistive Behavior in Conductive Polymer/MOF Composites},
journal = {Advanced Materials},
pages = {2312382},
issn = {0935-9648},
doi = {10.1002/adma.202312382},
year = {2024}
}
Metal-organic frameworks (MOFs) are promising materials for gas sensing but are often limited to single-use detection. A hybridization strategy is demonstrated synergistically deploying conductive MOFs (cMOFs) and conductive polymers (cPs) as two complementary mixed ionic-electronic conductors in high-performing stand-alone chemiresistors. This work presents significant improvement in i) sensor recovery kinetics, ii) cycling stability, and iii) dynamic range at room temperature. The effect of hybridization across well-studied cMOFs is demonstrated based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexaiminotriphenylene (HITP) ligands with varied metal nodes (Co, Cu, Ni). A comprehensive mechanistic study is conducted to relate energy band alignments at the heterojunctions between the MOFs and the polymer with sensing thermodynamics and binding kinetics. The findings reveal that hole enrichment of the cMOF component upon hybridization leads to selective enhancement in desorption kinetics, enabling significantly improved sensor recovery at room temperature, and thus long-term response retention. This mechanism is further supported by density functional theory calculations on sorbate–analyte interactions. It is also found that alloying cPs and cMOFs enables facile thin film co-processing and device integration, potentially unlocking the use of these hybrid conductors in diverse electronic applications.
@article{RN3,
author = {Ahmad, Bayu IZ and Jerozal, Ronald T and Meng, Sijing and Oh, Changwan and Cho, Yeongsu and Kulik, Heather J and Lambert, Tristan H and Milner, Phillip J},
title = {Defect-Engineered Metal–Organic Frameworks as Bioinspired Heterogeneous Catalysts for Amide Bond Formation},
journal = {Journal of the American Chemical Society},
volume = {146},
number = {50},
pages = {34743-34752},
issn = {0002-7863},
doi = {10.1021/jacs.4c13196},
year = {2024}
}
The synthesis of amides from amines and carboxylic acids is the most widely carried out reaction in medicinal chemistry. Yet, most amide couplings are still conducted using stoichiometric reagents, leading to significant waste; few synthetic catalysts for this transformation have been adopted industrially due to their limited scope and/or poor recyclability. The majority of catalytic approaches focus on a single activation mode, such as enhancing the electrophilicity of the carboxylic acid partner using a Lewis acid. In contrast, nature effortlessly forges and breaks amide bonds using precise arrays of Lewis/Brønsted acidic and basic functional groups. Drawing inspiration from these systems, herein we report a simple defect engineering strategy to colocalize Lewis acidic Zr sites with other catalytically active species within porous metal–organic frameworks (MOFs). Specifically, the combination of pyridine N-oxide and Zr open metal sites within the defective framework MOF-808-py-Nox produces a heterogeneous catalyst that facilitates amide bond formation with broad functional group compatibility from amines and carboxylic acids, esters, or primary amides. Extensive density functional theory (DFT) calculations using cluster models support that the formation of a hydrogen-bonding network at the defect sites facilitates amide bond formation in this material. MOF-808-py-Nox can be recycled at least five times without losing significant crystallinity, porosity, or catalytic activity and can be employed in continuous flow. This defect engineering strategy can be potentially generalized to produce libraries of catalytically active MOFs with different combinations of colocalized functional groups.
@article{RN8,
author = {Ariyarathna, Isuru R and Cho, Yeongsu and Duan, Chenru and Kulik, Heather J},
title = {Gas-phase and solid-state electronic structure analysis and DFT benchmarking of HfCO},
journal = {Physical Chemistry Chemical Physics},
volume = {25},
number = {39},
pages = {26632-26639},
doi = {10.1039/D3CP03550F},
year = {2023}
}
Ab initio multi-reference configuration interaction (MRCI) and coupled cluster singles doubles and perturbative triples [CCSD(T)] levels of theory were used to study ground and excited electronic states of HfCO. We report potential energy curves, dissociation energies (De), excitation energies, harmonic vibrational frequencies, and chemical bonding patterns of HfCO. The 3Σ− ground state of HfCO has an 1σ22σ21π2 electron configuration and a ∼30 kcal mol−1 dissociation energy with respect to its lowest-energy fragments Hf(3F) + CO(X1Σ+). We further evaluated the De of its isovalent HfCX (X = S, Se, Te, Po) series and observed that they increase linearly from the lighter HfCO to the heavier HfCPo with the dipole moment of the CX ligand. The same linear relationship was observed for TiCX and ZrCX. We utilized the CCSD(T) benchmark values of De, excitation energy, and ionization energy (IE) values to evaluate density functional theory (DFT) errors with 23 exchange–correlation functionals spanning GGA, meta-GGA, global GGA hybrid, meta-GGA hybrid, range-separated hybrid, and double-hybrid functional families. The global GGA hybrid B3LYP and range-separated hybrid ωB97X performed well at representing the ground state properties of HfCO (i.e., De and IE). Finally, we extended our DFT analysis to the interaction of a CO molecule with a Hf surface and observed that the surface chemisorption energy and the gas-phase molecular dissociation energy are very similar for some DFAs but not others, suggesting moderate transferability of the benchmarks on these molecules to the solid state.
@article{RN6,
author = {Ziegler, Jonas D and Cho, Yeongsu and Terres, Sophia and Menahem, Matan and Taniguchi, Takashi and Watanabe, Kenji and Yaffe, Omer and Berkelbach, Timothy C and Chernikov, Alexey},
title = {Mobile Trions in Electrically Tunable 2D Hybrid Perovskites},
journal = {Advanced Materials},
volume = {35},
number = {18},
pages = {2210221},
issn = {0935-9648},
doi = {10.1002/adma.202210221},
year = {2023}
}
2D hybrid perovskites are currently in the spotlight of material research for light-harvesting and -emitting applications. It remains extremely challenging, however, to externally control their optical response due to the difficulties of introducing electrical doping. Here, an approach of interfacing ultrathin sheets of perovskites with few-layer graphene and hexagonal boron nitride into gate-tunable, hybrid heterostructures, is demonstrated. It allows for bipolar, continuous tuning of light emission and absorption in 2D perovskites by electrically injecting carriers to densities as high as 1012 cm−2. This reveals the emergence of both negatively and positively charged excitons, or trions, with binding energies up to 46 meV, among the highest measured for 2D systems. Trions are shown to dominate light emission and propagate with mobilities reaching 200 cm2 V−1 s−1 at elevated temperatures. The findings introduce the physics of interacting mixtures of optical and electrical excitations to the broad family of 2D inorganic–organic nanostructures. The presented strategy to electrically control the optical response of 2D perovskites highlights it as a promising material platform toward electrically modulated light-emitters, externally guided charged exciton currents, and exciton transistors based on layered, hybrid semiconductors.
@article{RN5,
author = {Sakurada, Tomoaki and Cho, Yeongsu and Paritmongkol, Watcharaphol and Lee, Woo Seok and Wan, Ruomeng and Su, Annlin and Shcherbakov-Wu, Wenbi and Müller, Peter and Kulik, Heather J and Tisdale, William A},
title = {1D Hybrid Semiconductor Silver 2, 6-Difluorophenylselenolate},
journal = {Journal of the American Chemical Society},
volume = {145},
number = {9},
pages = {5183-5190},
issn = {0002-7863},
doi = {10.1021/jacs.2c11896},
year = {2023}
}
Organic–inorganic hybrid materials present new opportunities for creating low-dimensional structures with unique light–matter interaction. In this work, we report a chemically robust yellow emissive one-dimensional (1D) semiconductor, silver 2,6-difluorophenylselenolate─AgSePhF2(2,6), a new member of the broader class of hybrid low-dimensional semiconductors, metal–organic chalcogenolates. While silver phenylselenolate (AgSePh) crystallizes as a two-dimensional (2D) van der Waals semiconductor, introduction of fluorine atoms at the (2,6) position of the phenyl ring induces a structural transition from 2D sheets to 1D chains. Density functional theory calculations reveal that AgSePhF2 (2,6) has strongly dispersive conduction and valence bands along the 1D crystal axis. Visible photoluminescence centered around λp ≈ 570 nm at room temperature exhibits both prompt (110 ps) and delayed (36 ns) components. The absorption spectrum exhibits excitonic resonances characteristic of low-dimensional hybrid semiconductors, with an exciton binding energy of approximately 170 meV as determined by temperature-dependent photoluminescence. The discovery of an emissive 1D silver organoselenolate highlights the structural and compositional richness of the chalcogenolate material family and provides new insights for molecular engineering of low-dimensional hybrid organic–inorganic semiconductors.
@article{RN4,
author = {Dahl, Jakob C and Niblett, Samuel and Cho, Yeongsu and Wang, Xingzhi and Zhang, Ye and Chan, Emory M and Alivisatos, A Paul},
title = {Scientific Machine Learning of 2D Perovskite Nanosheet Formation},
journal = {Journal of the American Chemical Society},
volume = {145},
number = {42},
pages = {23076-23087},
issn = {0002-7863},
doi = {10.1021/jacs.3c05984},
year = {2023}
}
We apply a scientific machine learning (ML) framework to aid the prediction and understanding of nanomaterial formation processes via a joint spectral–kinetic model. We apply this framework to study the nucleation and growth of two-dimensional (2D) perovskite nanosheets. Colloidal nanomaterials have size-dependent optical properties and can be observed in situ, all of which make them a good model for understanding the complex processes of nucleation, growth, and phase transformation of 2D perovskites. Our results demonstrate that this model nanomaterial can form through two processes at the nanoscale: either via a layer-by-layer chemical exfoliation process from lead bromide nanocrystals or via direct nucleation from precursors. We utilize a phenomenological kinetic analysis to study the exfoliation process and scientific machine learning to study the direct nucleation and growth and discuss the circumstances under which it is more appropriate to use phenomenological or more complex machine learning models. Data for both analysis techniques are collected through in situ spectroscopy in a stopped flow chamber, incorporating over 500,000 spectra taken under more than 100 different conditions. More broadly, our research shows that the ability to utilize and integrate traditional kinetics and machine learning methods will greatly assist in the understanding of complex chemical systems.
@article{RN7,
author = {Biffi, Giulia and Cho, Yeongsu and Krahne, Roman and Berkelbach, Timothy C},
title = {Excitons and their fine structure in lead halide perovskite nanocrystals from atomistic GW/BSE calculations},
journal = {The Journal of Physical Chemistry C},
volume = {127},
number = {4},
pages = {1891-1898},
issn = {1932-7447},
doi = {10.1021/acs.jpcc.2c07111},
year = {2023}
}
Atomistically detailed computational studies of nanocrystals, such as those derived from the promising lead-halide perovskites, are challenging due to the large number of atoms and lack of symmetries to exploit. Here, focusing on methylammonium lead iodide nanocrystals, we combine a real-space tight binding model with the GW approximation to the self-energy and obtain exciton wave functions and absorption spectra via solutions of the associated Bethe–Salpeter equation. We find that the size dependence of carrier confinement, dielectric contrast, electron–hole exchange, and exciton binding energies has a strong impact on the lowest excitation energy, which can be tuned by almost 1 eV over the diameter range of 2–6 nm. Our calculated excitation energies are about 0.2 eV higher than experimentally measured photoluminescence, and they display the same qualitative size dependence. Focusing on the fine structure of the band-edge excitons, we find that the lowest-lying exciton is spectroscopically dark and about 20–30 meV lower in energy than the higher-lying triplet of the bright states whose degeneracy is slightly broken by crystal field effects.
@article{RN10,
author = {Lee, Woo Seok and Cho, Yeongsu and Powers, Eric R and Paritmongkol, Watcharaphol and Sakurada, Tomoaki and Kulik, Heather J and Tisdale, William A},
title = {Light Emission in 2D Silver Phenylchalcogenolates},
journal = {ACS nano},
volume = {16},
number = {12},
pages = {20318-20328},
issn = {1936-0851},
doi = {10.1021/acsnano.2c06204},
year = {2022}
}
Silver phenylselenolate (AgSePh, also known as “mithrene”) and silver phenyltellurolate (AgTePh, also known as “tethrene”) are two-dimensional (2D) van der Waals semiconductors belonging to an emerging class of hybrid organic–inorganic materials called metal–organic chalcogenolates. Despite having the same crystal structure, AgSePh and AgTePh exhibit a strikingly different excitonic behavior. Whereas AgSePh exhibits narrow, fast luminescence with a minimal Stokes shift, AgTePh exhibits comparatively slow luminescence that is significantly broadened and red-shifted from its absorption minimum. Using time-resolved and temperature-dependent absorption and emission microspectroscopy, combined with subgap photoexcitation studies, we show that exciton dynamics in AgTePh films are dominated by an intrinsic self-trapping behavior, whereas dynamics in AgSePh films are dominated by the interaction of band-edge excitons with a finite number of extrinsic defect/trap states. Density functional theory calculations reveal that AgSePh has simple parabolic band edges with a direct gap at Γ, whereas AgTePh has a saddle point at Γ with a horizontal splitting along the Γ-N1 direction. The correlation between the unique band structure of AgTePh and exciton self-trapping behavior is unclear, prompting further exploration of excitonic phenomena in this emerging class of hybrid 2D semiconductors.
@article{RN9,
author = {Cho, Yeongsu and Nandy, Aditya and Duan, Chenru and Kulik, Heather J},
title = {DFT-based multireference diagnostics in the solid state: Application to metal–organic frameworks},
journal = {Journal of Chemical Theory and Computation},
volume = {19},
number = {1},
pages = {190-197},
issn = {1549-9618},
doi = {10.1021/acs.jctc.2c01033},
year = {2022}
}
When a many-body wave function of a system cannot be captured by a single determinant, high-level multireference (MR) methods are required to properly explain its electronic structure. MR diagnostics to estimate the magnitude of such static correlation have been primarily developed for molecular systems and range from low in computational cost to as costly as the full MR calculation itself. We report the first application of low-cost MR diagnostics based on the fractional occupation number calculated with finite-temperature DFT to solid-state systems. To compare the behavior of the diagnostics on solids and molecules, we select metal–organic frameworks (MOFs) as model materials because their reticular nature provides an intuitive way to identify molecular derivatives. On a series of closed-shell MOFs, we demonstrate that the DFT-based MR diagnostics are equally applicable to solids as to their molecular derivatives. The magnitude and spatial distribution of the MR character of a MOF are found to have a good correlation with those of its molecular derivatives, which can be calculated much more affordably in comparison to those of the full MOF. The additivity of MR character discussed here suggests the set of molecular derivatives to be a good representation of a MOF for both MR detection and ultimately for MR corrections, facilitating accurate and efficient high-throughput screening of MOFs and other porous solids.
@article{RN11,
author = {Cho, Yeongsu and Bintrim, Sylvia J and Berkelbach, Timothy C},
title = {Simplified GW/BSE approach for charged and neutral excitation energies of large molecules and nanomaterials},
journal = {Journal of Chemical Theory and Computation},
volume = {18},
number = {6},
pages = {3438-3446},
issn = {1549-9618},
doi = {10.1021/acs.jctc.2c00087},
year = {2022}
}
Inspired by Grimmeʼs simplified Tamm–Dancoff density functional theory approach [Grimme, S. J. Chem. Phys. 2013, 138, 244104], we describe a simplified approach to excited-state calculations within the GW approximation to the self-energy and the Bethe–Salpeter equation (BSE), which we call sGW/sBSE. The primary simplification to the electron repulsion integrals yields the same structure as with tensor hypercontraction, such that our method has a storage requirement that grows quadratically with system size and computational timing that grows cubically with system size. The performance of sGW is tested on the ionization potential of the molecules in the GW100 test set, for which it differs from ab initio GW calculations by only 0.2 eV. The performance of sBSE (based on the sGW input) is tested on the excitation energies of molecules in Thielʼs set, for which it differs from ab initio GW/BSE calculations by about 0.5 eV. As examples of the systems that can be routinely studied with sGW/sBSE, we calculate the band gap and excitation energy of hydrogen-passivated silicon nanocrystals with up to 2650 electrons in 4678 spatial orbitals and the absorption spectra of two large organic dye molecules with hundreds of atoms.
@article{RN12,
author = {Cho, Yeongsu and Greene, Samuel M and Berkelbach, Timothy C},
title = {Simulations of trions and biexcitons in layered hybrid organic-inorganic lead halide perovskites},
journal = {Physical Review Letters},
volume = {126},
number = {21},
pages = {216402},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.126.216402},
year = {2021}
}
Behaving like atomically precise two-dimensional quantum wells with non-negligible dielectric contrast, the layered hybrid organic-inorganic lead halide perovskites (HOIPs) have strong electronic interactions leading to tightly bound excitons with binding energies on the order of 500 meV. These strong interactions suggest the possibility of larger excitonic complexes like trions and biexcitons, which are hard to study numerically due to the complexity of the layered HOIPs. Here, we propose and parametrize a model Hamiltonian for excitonic complexes in layered HOIPs and we study the correlated eigenfunctions of trions and biexcitons using a combination of diffusion Monte Carlo and very large variational calculations with explicitly correlated Gaussian basis functions. Binding energies and spatial structures of these complexes are presented as a function of the layer thickness. The trion and biexciton of the thinnest layered HOIP have binding energies of 35 and 44 meV, respectively, whereas a single exfoliated layer is predicted to have trions and biexcitons with equal binding energies of 48 meV. We compare our findings to available experimental data and to that of other quasi-two-dimensional materials.
@article{RN13,
author = {Wiscons, Ren A and Cho, Yeongsu and Han, Sae Young and Dismukes, Avalon H and Meirzadeh, Elena and Nuckolls, Colin and Berkelbach, Timothy C and Roy, Xavier},
title = {Polytypism, anisotropic transport, and Weyl nodes in the van der Waals metal TaFeTe4},
journal = {Journal of the American Chemical Society},
volume = {143},
number = {1},
pages = {109-113},
issn = {0002-7863},
doi = {10.1021/jacs.0c11674},
year = {2020}
}
Layered van der Waals (vdW) materials belonging to the MM′Te4 structure class have recently received intense attention due to their ability to host exotic electronic transport phenomena, such as in-plane transport anisotropy, Weyl nodes, and superconductivity. Here we report two new vdW materials with strongly anisotropic in-plane structures featuring stripes of metallic TaTe2 and semiconducting FeTe2, α-TaFeTe4 and β-TaFeTe4. We find that the structure of α-TaFeTe4 produces strongly anisotropic in-plane electronic transport (anisotropy ratio of up to 250%), outcompeting all other vdW metals, and demonstrate that it can be mechanically exfoliated to the two-dimensional (2D) limit. We also explore the possibility that broken inversion symmetry in β-TaFeTe4 produces Weyl points in the electronic band structure. Eight Weyl nodes slightly below the Fermi energy are computationally identified for β-TaFeTe4, indicating they may contribute to the transport behavior of this polytype. These findings identify the TaFeTe4 polytypes as an ideal platform for investigation of 2D transport anisotropy and chiral charge transport as a result of broken symmetry.
@article{RN15,
author = {Zhou, Qunfei and Cho, Yeongsu and Yang, Shenyuan and Weiss, Emily A and Berkelbach, Timothy C and Darancet, Pierre},
title = {Large band edge tunability in colloidal nanoplatelets},
journal = {Nano letters},
volume = {19},
number = {10},
pages = {7124-7129},
issn = {1530-6984},
doi = {10.1021/acs.nanolett.9b02645},
year = {2019}
}
We study the impact of organic surface ligands on the electronic structure and electronic band edge energies of quasi-two-dimensional (2D) colloidal cadmium selenide nanoplatelets (NPLs) using density functional theory. We show how control of the ligand and ligand–NPL interface dipoles results in large band edge energy shifts, over a range of 5 eV for common organic ligands with a minor effect on the NPL band gaps. Using a model self-energy to account for the dielectric contrast and an effective mass model of the excitons, we show that the band edge tunability of NPLs together with the strong dependence of the optical band gap on NPL thickness can lead to favorable photochemical and optoelectronic properties.
@article{RN16,
author = {Raja, Archana and Waldecker, Lutz and Zipfel, Jonas and Cho, Yeongsu and Brem, Samuel and Ziegler, Jonas D and Kulig, Marvin and Taniguchi, Takashi and Watanabe, Kenji and Malic, Ermin and Heinz, Tony F and Berkelbach, Timothy C and Chernikov, Alexey},
title = {Dielectric disorder in two-dimensional materials},
journal = {Nature nanotechnology},
volume = {14},
number = {9},
pages = {832-837},
issn = {1748-3387},
doi = {10.1038/s41565-019-0520-0},
year = {2019}
}
Understanding and controlling disorder is key to nanotechnology and materials science. Traditionally, disorder is attributed to local fluctuations of inherent material properties such as chemical and structural composition, doping or strain. Here, we present a fundamentally new source of disorder in nanoscale systems that is based entirely on the local changes of the Coulomb interaction due to fluctuations of the external dielectric environment. Using two-dimensional semiconductors as prototypes, we experimentally monitor dielectric disorder by probing the statistics and correlations of the exciton resonances, and theoretically analyse the influence of external screening and phonon scattering. Even moderate fluctuations of the dielectric environment are shown to induce large variations of the bandgap and exciton binding energies up to the 100 meV range, often making it a dominant source of inhomogeneities. As a consequence, dielectric disorder has strong implications for both the optical and transport properties of nanoscale materials and their heterostructures.
@article{RN14,
author = {Cho, Yeongsu and Berkelbach, Timothy C},
title = {Optical properties of layered hybrid organic–inorganic halide perovskites: a tight-binding GW-BSE study},
journal = {The journal of physical chemistry letters},
volume = {10},
number = {20},
pages = {6189-6196},
issn = {1948-7185},
doi = {10.1021/acs.jpclett.9b02491},
year = {2019}
}
We present a many-body calculation of the band structure and optical spectrum of the layered hybrid organic–inorganic halide perovskites in the Ruddlesden–Popper phase with the general formula A2′An–1MnX3n+1, where n controls the thickness of the primarily inorganic perovskite layers. We calculate the mean-field band structure with spin–orbit coupling, quasi-particle corrections within the GW approximation, and optical spectra using the Bethe–Salpeter equation. The model is parametrized by first-principles calculations and classical electrostatic screening, enabling an accurate but cost-effective study of large unit cells and corresponding n-dependent properties. A transition of the electronic and optical properties from quasi-two-dimensional behavior to three-dimensional behavior is shown for increasing n, and the nonhydrogenic character of the excitonic Rydberg series is analyzed. For methylammonium lead iodide perovskites with butylammonium spacers, our n-dependent 1s and 2s exciton energy levels are in good agreement with those from recently reported experiments, and the 1s exciton binding energy is calculated to be 302 meV for n = 1, 97 meV for n = 5, and 37 meV for n = ∞ (bulk MAPbI3). A calculation for an exfoliated n = 1 bilayer predicts a very large 1s exciton binding energy of 444 meV.
@article{RN17,
author = {Cho, Yeongsu and Berkelbach, Timothy C},
title = {Environmentally sensitive theory of electronic and optical transitions in atomically thin semiconductors},
journal = {Physical Review B},
volume = {97},
number = {4},
pages = {041409},
issn = {2469-9950},
doi = {10.1103/PhysRevB.97.041409},
year = {2018}
}
We present an electrostatic theory of band-gap renormalization in atomically thin semiconductors that captures the strong sensitivity to the surrounding dielectric environment. In particular, our theory aims to correct known band gaps, such as that of the three-dimensional bulk crystal. Combining our quasiparticle band gaps with an effective-mass theory of excitons yields environmentally sensitive optical gaps as would be observed in absorption or photoluminescence. For an isolated monolayer of MoS2, the presented theory is in good agreement with ab initio results based on the ?? approximation and the Bethe-Salpeter equation. We find that changes in the electronic band gap are almost exactly offset by changes in the exciton binding energy such that the energy of the first optical transition is nearly independent of the electrostatic environment, rationalizing experimental observations.
Cho Research Group
Department of Chemistry
University of Houston
ycho12@uh.edu
University of Houston
3585 Cullen Blvd. Rm 221
Houston, TX 77204
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