Development of effective stochastic potential method using random matrix theory for efficient conformational sampling of semiconductor nanoparticles at non-zero temperatures

Scher, Jeremy; Bayne, Michael G.; Srihari, Amogh; Nangia, Shikha; Chakraborty, Arindam

doi:10.1063/1.5026027

Cited by 7 publications

(9 citation statements)

References 54 publications

(63 reference statements)

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“…A qualitatively correct picture will need to accommodate both the bright bulk-to-bulk PiS-like states as well as a dense manifold of surface-associated states. At present there are no simple models that can accomplish this, although recent results using random matrix theory 64 are potentially one good first step.…”

Section: Discussionmentioning

confidence: 99%

Colloidal CdSe nanocrystals are inherently defective

2021

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Colloidal CdSe nanocrystals (NCs) have shown promise in applications ranging from LED displays to medical imaging. Their unique photophysics depend sensitively on the presence or absence of surface defects. Using simulations, we show that CdSe NCs are inherently defective; even for stoichiometric NCs with perfect ligand passivation and no vacancies or defects, we still observe that the low energy spectrum is dominated by dark, surface-associated excitations, which are more numerous in larger NCs. Surface structure analysis shows that the majority of these states involve holes that are localized on two-coordinate Se atoms. As chalcogenide atoms are not passivated by any Lewis base ligand, varying the ligand should not dramatically change the number of dark states, which we confirm by simulating three passivation schemes. Our results have significant implications for understanding CdSe NC photophysics, and suggest that photochemistry and short-range photoinduced charge transfer should be much more facile than previously anticipated.

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Section: Discussionmentioning

confidence: 99%

Colloidal CdSe nanocrystals are inherently defective

2021

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“…This phenomenon is caused by the quantum confinement of elementary excitations in such small objects. In this context, semiconductor nanocrystals have a size-tunable optical gap, which makes them promising candidates in all applications related to the absorption and emission of light [4][5][6][7][8][9]. Along with a high luminescence efficiency attainable in quantum dots (QDs), the key parameter is also the half-width of the optical bands, which largely determines the possibility of their use.…”

Section: Introductionmentioning

confidence: 99%

Inhomogeneous Broadening of the Exciton Band in Optical Absorption Spectra of InP/ZnS Nanocrystals

Savchenko

Weinstein

2019

Nanomaterials

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In this work, we have simulated the processes of broadening the first exciton band in optical absorption spectra (OA) for InP/ZnS ensembles of colloidal quantum dots (QDs). A phenomenological model has been proposed that takes into account the effects of the exciton–phonon interaction, and allows one to analyze the influence of the static and dynamic types of atomic disorder on the temperature changes in the spectral characteristics in question. To vary the degree of static disorder in the model system, we have used a parameter δ, which characterizes the QD dispersion in size over the ensemble. We have also calculated the temperature shifts of the maxima and changes in the half-width for the exciton peaks in single nanocrystals (δ = 0), as well as for the integrated OA bands in the QD ensembles with different values of δ = 0.6–17%. The simulation results and the OA spectra data measured for InP/ZnS nanocrystals of 2.1 nm (δ = 11.1%) and 2.3 nm (δ = 17.3%), are in good mutual agreement in the temperature range of 6.5 K–RT. It has been shown that the contribution of static disorder to the observed inhomogeneous broadening of the OA bands for the QDs at room temperature exceeds 90%. The computational experiments performed indicate that the temperature shift of the maximum for the integrated OA band coincides with that for the exciton peak in a single nanocrystal. In this case, a reliable estimate of the parameters of the fundamental exciton–phonon interaction can be made. Simultaneously, the values of the specified parameters, calculated from the temperature broadening of the OA spectra, can be significantly different from the true ones due to the effects of static atomic disorder in real QD ensembles.

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“…In recent studies, it has been estimated that a sample size on the order of 10 5 −10 6 is needed to obtain ensemble-averaged properties to within chemical accuracy. 3,4 The problem is further exacerbated for excited-state properties, which have traditionally been more computationally demanding than ground-state calculations.…”

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confidence: 99%

“…The complete mathematical derivation and the implementation details of the ground-state ESP method were presented earlier in ref 4, and summary of the key concepts are presented here to avoid repetition. The Fock matrix associated with the effective stochastic potential (ESP) method 4 is given by…”

mentioning

confidence: 99%

“…Generation of a distribution of QM properties from first-principles calculations is especially challenging because of the high computational cost associated with performing calculations on a large sample size to obtain reliable statistics. In recent studies, it has been estimated that a sample size on the order of 10 5 –10 6 is needed to obtain ensemble-averaged properties to within chemical accuracy. , The problem is further exacerbated for excited-state properties, which have traditionally been more computationally demanding than ground-state calculations.…”

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confidence: 99%

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Evidence of Skewness and Sub-Gaussian Character in Temperature-Dependent Distributions of One Million Electronic Excitation Energies in PbS Quantum Dots

Scher

Govind

Chakraborty

2020

J. Phys. Chem. Lett.

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Obtaining statistical distributions by sampling a large number of conformations is vital for an accurate description of temperature-dependent properties of chemical systems. However, constructing distributions with 10 5 −10 6 samples is computationally challenging because of the prohibitively high computational cost of performing first-principles quantum mechanical calculations. In this work, we present a new technique called the effective stochastic potential configuration interaction singles (ESP-CIS) method to obtain excitation energies. The ESP-CIS method uses random matrix theory for the construction of an effective stochastic representation of the Fock operator and combines it with the CIS method. Excitedstate energies of PbS quantum dots (0.75−1.75 nm) at temperatures of 10−400 K were calculated using the ESP-CIS method. Results from a total of 27 million excitation energy calculations revealed the distributions to be sub-Gaussian in nature with negative skewness, which progressively became red-shifted with increasing temperature. This study demonstrates the efficacy of the ESP-CIS method as a general-purpose method for efficient excited-state calculations.

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Development of effective stochastic potential method using random matrix theory for efficient conformational sampling of semiconductor nanoparticles at non-zero temperatures

Cited by 7 publications

References 54 publications

Colloidal CdSe nanocrystals are inherently defective

Colloidal CdSe nanocrystals are inherently defective

Inhomogeneous Broadening of the Exciton Band in Optical Absorption Spectra of InP/ZnS Nanocrystals

Evidence of Skewness and Sub-Gaussian Character in Temperature-Dependent Distributions of One Million Electronic Excitation Energies in PbS Quantum Dots

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