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DOE OSTI2025

End-of-Century Changes in Orographic Precipitation with the Intermediate Complexity Atmospheric Research Model over the Western United States

Abstract Downscaled precipitation projections were created using the Intermediate Complexity Atmospheric Research (ICAR) model over the western United States to increase the physical realism in orographic precipitation changes. End-of-century simulations from eight models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) were downscaled with ICAR and compared to the widely utilized statistically downscaled dataset, localized constructed analogs (LOCAs), to understand where and why projections of cool-season (September–May) precipitation differed. ICAR and LOCA precipitation projections were similar, but their sign differed in hydrologically relevant regions likely due to ICAR’s simulation of microphysics and mesoscale dynamics with high-resolution topography (6 km). In the Pacific Northwest, cool-season precipitation projections from ICAR showed an increase on the windward side of the Cascades and no significant change within the lee. This difference between the windward and leeward side was attributed to reduced zonal wind speeds, allowing more time for microphysical processes within ICAR. This contrast is enhanced by rain’s faster fall speed compared to snow, limiting transport into the lee. Meanwhile, LOCA projected an increase in precipitation across the Cascades. In the Upper Colorado River basin, LOCA projected an increase in precipitation in high elevation regions (>3000 m), but ICAR projected no significant change or a decrease in precipitation. High elevation differences were most evident in the spring and fall and were also attributed to a snow-to-rain transition and dynamical processes that impacted orographic enhancement within ICAR. Idealized, controlled studies are needed to better isolate individual processes, but these results underscore the importance of including microphysics and mesoscale dynamics within regional-scale precipitation projections. Significance Statement A set of global climate model simulations was downscaled using an atmospheric model that contains key physical equations, referred to as Intermediate Complexity Atmospheric Research (ICAR). ICAR was used to examine projected changes in end-of-century cool-season precipitation over mountains in the western United States. Precipitation projections from ICAR were similar to projections that used statistical relationships to downscale climate projections. However, projections differed between ICAR and statistically downscaled datasets in whether they increased, decreased, or stayed the same in specific, hydrologically relevant regions such as the eastern Cascades and high elevation areas of the Upper Colorado River basin. These differences were attributed to the simulation of physical processes in ICAR. The results highlight the importance of kilometer-scale atmospheric processes in regional climate projections.

Currier, William Ryan [NOAA/Physical Sciences Labo↗

DOE OSTI2020

Towards scalable dataframe systems

Dataframes are a popular abstraction to represent, prepare, and analyze data. Despite the remarkable success of dataframe libraries in R and Python, dataframes face performance issues even on moderately large datasets. Moreover, there is significant ambiguity regarding dataframe semantics. In this paper we lay out a vision and roadmap for scalable dataframe systems. To demonstrate the potential in this area, we report on our experience building Modin, a scaled-up implementation of the most widely-used and complex dataframe API today, Python's pandas. With pandas as a reference, we propose a simple data model and algebra for dataframes to ground discussion in the field. Given this foundation, we lay out an agenda of open research opportunities where the distinct features of dataframes will require extending the state of the art in many dimensions of data management. We discuss the implications of signature dataframe features including flexible schemas, ordering, row/column equivalence, and data/metadata fluidity, as well as the piecemeal, trial-and-error-based approach to interacting with dataframes.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2011

Community Wind: Once Again Pushing the Envelope of Project Finance

In the United States, the 'community wind' sector - loosely defined here as consisting of relatively small utility-scale wind power projects that sell power on the wholesale market and that are developed and owned primarily by local investors - has historically served as a 'test bed' or 'proving grounds' for up-and-coming wind turbine manufacturers that are trying to break into the U.S. wind power market. For example, community wind projects - and primarily those located in the state of Minnesota - have deployed the first U.S. installations of wind turbines from Suzlon (in 2003), DeWind (2008), Americas Wind Energy (2008) and later Emergya Wind Technologies (2010), Goldwind (2009), AAER/Pioneer (2009), Nordic Windpower (2010), Unison (2010), and Alstom (2011). Thus far, one of these turbine manufacturers - Suzlon - has subsequently achieved some success in the broader U.S. wind market as well. Just as it has provided a proving grounds for new turbines, so too has the community wind sector served as a laboratory for experimentation with innovative new financing structures. For example, a variation of one of the most common financing arrangements in the U.S. wind market today - the special allocation partnership flip structure (see Figure 1 in Section 2.1) - was first developed by community wind projects in Minnesota more than a decade ago (and is therefore sometimes referred to as the 'Minnesota flip' model) before being adopted by the broader wind market. More recently, a handful of community wind projects built over the past year have been financed via new and creative structures that push the envelope of wind project finance in the U.S. - in many cases, moving beyond the now-standard partnership flip structures involving strategic tax equity investors. These include: (1) a 4.5 MW project in Maine that combines low-cost government debt with local tax equity, (2) a 25.3 MW project in Minnesota using a sale/leaseback structure, (3) a 10.5 MW project in South Dakota financed by an intrastate offering of both debt and equity, (4) a 6 MW project in Washington state that taps into New Markets Tax Credits using an 'inverted' or 'pass-through' lease structure, and (5) a 9 MW project in Oregon that combines a variety of state and federal incentives and loans with unconventional equity from high-net-worth individuals. In most cases, these are first-of-their-kind structures that could serve as useful examples for other projects - both community and commercial wind alike. This report describes each of these innovative new financing structures in some detail, using a case-study approach. The purpose is twofold: (1) to disseminate useful information on these new financial structures, most of which are widely replicable; and (2) to highlight the recent policy changes - many of them temporary unless extended - that have facilitated this innovation. Although the community wind market is currently only a small sub-sector of the U.S. wind market - as defined here, less than 2% of the overall market at the end of 2009 (Wiser and Bolinger 2010) - its small size belies its relevance to the broader market. As such, the information provided in this report has relevance beyond its direct application to the community wind sector. The next two sections of this report briefly summarize how most community wind projects in the U.S. have been financed historically (i.e., prior to this latest wave of innovation) and describe the recent federal policy changes that have enabled a new wave of financial innovation to occur, respectively. Section 4 contains brief case studies of how each of the five projects mentioned above were financed, noting the financial significance of each. Finally, Section 5 concludes by distilling a number of general observations or pertinent lessons learned from the experiences of these five projects.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2012

Operational and Compositional Factors that Affect the Performance Properties of ARP/MCU Saltstone Grout

The Saltstone Production Facility (SPF) receives low level waste (LLW) salt solution from Tank 50H for treatment and disposal. Tank 50H receives transfers from the Effluent Treatment Project (ETP), the H-Canyon General Purpose Evaporator, and the Actinide Removal Process/Modular Caustic Side Solvent Extraction Unit (ARP/MCU) Decontaminated Salt Solution Hold Tank (DSS-HT). At the SPF, the LLW is mixed with premix (a cementitious mixture of portland cement (PC), blast furnace slag (BFS) and Class F fly ash (FA)) in a Readco mixer to produce fresh (uncured) saltstone that is transferred to the Saltstone Disposal Facility (SDF) vaults. The saltstone formulation (mix design) must produce a grout waste form that meets both placement and performance properties. In previous simulated saltstone studies, multiple compositional factors were identified that drive the performance properties of saltstone made from the projected ARP/MCU salt solution. This composition was selected as salt solution simulant since ARP/MCU is the primary influent into Tank 50H. The primary performance property investigated was hydraulic conductivity since it is a variable input property to the saltstone Performance Assessment (PA) transport model. In addition, the porosity, also referred to as void structure, is another variable that impacts the PA response. In addition, Young's modulus and cured density are other performance properties analyzed in this report; however they are indicators of the performance of saltstone and not direct inputs into the PA. The data from previous studies showed that the largest impact on the performance properties of saltstone was due to curing temperature, followed by aluminate concentration in the salt solution, water to premix ratio and premix composition. However, due to the scope of the previous studies, only a few mixes were cured and analyzed at higher temperatures. The samples cured at 60°C had an increased hydraulic conductivity of approximately 600 times that of the sample cured at room temperature. The hydration reactions initiated during the mixing of the premix and salt solution continue during the curing period in the vaults to produce the hardened waste form product. The heat generated from exothermic hydration reactions results in a temperature increase in the vaults that depends on the composition of the decontaminated salt solution being dispositioned, the grout formulation (mix design) and the pour frequency and volume. This heat generation is a contributing factor to the temperature increase in the vaults that leads to an increased cure temperature for the grout. This report will further investigate the impact of curing temperature on saltstone performance properties (hydraulic conductivity, Young's modulus, porosity, etc.) over a range of aluminate concentration, water to premix (w/p) ratio and weight percent fly ash in the premix processed at the SPF. The three curing temperatures selected for this study were chosen to provide data at fixed cure temperatures that represent measured temperatures in the SDF vaults. This does not represent the conditions in the vault where the temperature of the saltstone is continually changing with time. For example, it may take several days for the saltstone to reach 60°C at a given elevation. Previous results demonstrated that the rates at which a selected curing temperature is reached affect the performance properties. The approach taken in this task, a rapid increase to the curing temperature, may be conservative with respect to decreased performance. Nevertheless, the data will provide a basis from which to determine the impact of curing temperature on saltstone performance as a function of key variables. A statistical evaluation of the results for these mixes will be performed to provide the range, and associated uncertainties, of hydraulic conductivity and other properties over this factor space.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2011

Irradiation Planning for Fully-Ceramic Micro-encsapsulated fuel in ATR at LWR-relevant conditions: year-end report on FY-2011

This report presents the estimation of required ATR irradiation levels for the DB-FCM fuel design (fueled with Pu and MAs). The fuel and assembly designs are those considered in a companion report [R. S. Sen et al., FCR&D-2011- 00037 or INL/EXT-11-23269]. These results, pertaining to the DB-FCM fuel, are definitive in as much as the design of said fuel is definitive. In addition to the work performed, as required, for DB-FCM fuel, work has started in a preliminary fashion on single-cell UO2 and UN fuels. These latter activities go beyond the original charter of this project and although the corresponding work is incomplete, significant progress has been achieved. However, in this context, all that has been achieved is only preliminary because the corresponding fuel designs are neither finalized nor optimized. In particular, the UO2 case is unlikely to result in a viable fuel design if limited to enrichment at or under 20 weight % in U-235. The UN fuel allows reasonable length cycles and is likely to make an optimal design possible. Despite being limited to preliminary designs and offering only preliminary conclusions, the irradiation planning tasks for UO2 and UN fuels that are summarized in this report are useful to the overall goal of devising and deploying FCM-LWR fuel since the methods acquired and tested in this project and the overall procedure for planning will be available for planning tests for the finalized fuel design. Indeed, once the fuel design is finalized and the expected burnup level is determined, the methodology that has been assembled will allow the prompt finalization of the neutronic planning of the irradiation experiment and would provide guidance on the expected experimental performance of the fuel. Deviations from the expected behavior will then have to be analyzed and the outcome of the analysis may be corrections or modifications for the assessment models as well as, possibly, fuel design modifications, and perhaps even variation of experimental control for future experimental phases. Besides the prediction of irradiation times, preliminary work was carried out on other aspects of irradiation planning. In particular, a method for evaluating the interplay of depletion, material performance modeling and irradiation is identified by reference to a companion report. Another area that was addressed in a preliminary fashion is the identification and selection of a strategy for the physical and mechanical design of the irradiation experiments. The principal conclusion is that the similarity between the FCM fuel and the fuel compacts of the Next Generation Nuclear Plant prismatic design are strong enough to warrant using irradiation hardware designs and instrumentation adapted from the AGR irradiation tests. Modifications, if found necessary, will probably be few and small, except as pertains to the water environment and its implications on the use of SiC cladding or SiC matrix with no additional cladding.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2015

Measurement of the neutron spectrum and ambient neutron dose rate equivalent from the small 252 Cf source at 1 meter

NASA Langley Research Center requested a measurement of the neutron spectral distribution and fluence from the 252 Cf source (model NS-120, LLNL serial # 7001677, referred as the SMALL Cf source) and determination of the ambient neutron dose rate equivalent and kerma at 100 cm for the Radiation Budget Instrument Experiment (Rad-X). The dosimetric quantities should be based on the neutron spectrum and the current neutron-to-dose conversion coefficients.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2018

Solid Mechanics Code Verification: Contrasting Classical and Manufactured Reference Solutions

Verification results for Sierra/SM using inexact reference solutions have often exhibited unsatisfactory convergence behavior. With an understanding of the convergence behavior for these types of tests, one can avoid falsely attributing pathologies of the test with incorrectness of the code. Simple theoretical results highlight that for an inexact reference solution two conditions must be met to observe asymptotic convergence. These conditions, and the resulting types of convergence behaviors, are further illustrated with graphical examples depicting the exact, inexact reference, and sequence of numerical solutions as vectors (in a function space). A stress concentration problem is adopted to contrast convergence behaviors when using inexact (classical linear elastic) and exact (manufactured) reference solutions. Convergence is not initially attained with the classical solution. Convergence with the manufactured solution indicates the convergence failure with the classical reference did not result from code error and provides insight on how for this problem asymptotic convergence could be attained with the classical reference solution by modifying the computational models.

42 ENGINEERING↗

DOE OSTI2018

Integrated Computational Study of Radiation Damage Effects in Grade 92 Steel and Alloy 709

Radiation resistance of austenitic alloy 709 (named as A709) and ferritic-martensitic steel Grade 92 (G92) were investigated in this project using 316H and Grade 91 (G91) as references, respectively. In the meantime, a model 709 (M709) alloy (Fe-20Cr-24Ni) was prepared to study the matrix response to irradiation. Samples machined from the tab section of three creep-ruptured A709 samples, i.e., 17,106 h at 600 °C, 12,014 h at 650 °C, and 16,448 h at 700 °C, were included in this work to evaluate radiation effect on the long-term “thermally aged” samples. Primarily Fe 2+ ion irradiation was conducted at 350, 600 and 670 °C for up to 75 displacements per atom (dpa), together with a few proton irradiation experiments at 380–670 °C for up to 1.5 dpa. Additionally, four neutron-irradiated NF709 samples (3.22–8 dpa at ~430–469 °C) were examined. The samples were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) for microstructures and nanoindentation for radiation-hardening. Unlike the negligible hardening after irradiation at 670 °C, irradiation to nominal 2.5–50 dpa at 350 °C resulted in radiation-hardening of 13.5±5.4 % for A709, which was comparable to that of 13.4±6.2 % for M709 and moderately lower than that of 20.1±5.6 % for 316H. The radiation-hardening induced by the same irradiation condition to the “thermally aged” samples was comparable to A709, which were hardened by 15.0±8.2 %, 13.5±6.0 %, and 10.1±6.1 % for the 600, 650, and 700 °C aged samples, respectively. The radiation-hardening of A709 is significantly lower than that (~94±9 %) of neutron-irradiated NF709 to 8 dpa at ~430 °C.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Difference distributions applicable to certain health physic's measurements

This paper discusses calculational methods for the determination of the difference distributions associated with certain health physics measurements. These measurements include the check source response counts relative to an initial reference count, the Albatross (i.e., HPI model 2080B) neutron tube counts relative to the gamma tube counts, and those that involve the use of the automatic background subtraction feature within portable health physics instrumentation. This paper therefore provides a technical basis for the necessary source strength of a check source in order to meet daily limits, the gamma field limitations of the HPI2080 Albatross, as well as the consequences of automatic background subtraction. Examples are provided that illustrate the methods for a few specific measurements.

61 RADIATION PROTECTION AND DOSIMETRY↗

DOE OSTI2018

Integrated Computational Study of Radiation Damage Effects in Grade 92 Steel and Alloy 709

36 MATERIALS SCIENCE↗

DOE OSTI2021

Fundamental 235 Uranium Nuclear Resonance Spectroscopy (End of Year Report)

Uranium-235 is ubiquitous in the nuclear industry however, detailed characterization by magnetic resonance spectroscopy has remained largely elusive to-date. Conventional nuclear magnetic resonance techniques are ill-suited for characterizing 235 U due to the small gyromagnetic ratio and extremely large quadrupole moment of this spin$^{7}$ /2 isotope. Thus, we have designed and built a high-frequency nuclear quadrupole resonance spectrometer for measuring the quadrupole resonance of this important isotope. A successful nuclear quadrupole resonance measurement of 235 U would be a significant accomplishment and could yield valuable physical parameters such as chemical shifts, local electric field gradients, and through-bond and through-space internuclear couplings, all of which are directly related to local structure. These terms can be used to understand structural details of poorly characterized uranium materials and can improve computational models of uranium for which accurate reference data is lacking

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2022

Design Methods, Tools, and Data for Ceramic Solar Receivers Year 1 Continuation Report

This report describes the first year of work on a project to develop the methods, tools, and data required to analyze high temperature ceramic Concentrating Solar Power (CSP) components. This first year focused on developing the methods and data required for a time-independent assessment of potential components, focusing in particular on ceramic solar receivers. The report describes both model development and testing work focused on accomplishing this goal. Our overall conclusion is that high temperature ceramic CSP components are viable and could provide a means to overcome the expected low reliability and short service life for equivalent components constructed from Ni-based superalloys. Based on the results reported here, we recommend the project continue to Phase II which will develop more sophisticated, realistic models for time-dependent failure of ceramics operating in expected CSP component conditions and develop the time-dependent ceramic test data needed to parameterize these models, using commercial SiC as a reference material.

14 SOLAR ENERGY↗

DOE OSTI2023

BUQEYE guide to projection-based emulators in nuclear physics

The BUQEYE collaboration (Bayesian Uncertainty Quantification: Errors in Your effective field theory) presents a pedagogical introduction to projection-based, reduced-order emulators for applications in low-energy nuclear physics. The term emulator refers here to a fast surrogate model capable of reliably approximating high-fidelity models. As the general tools employed by these emulators are not yet well-known in the nuclear physics community, we discuss variational and Galerkin projection methods, emphasize the benefits of offline-online decompositions, and explore how these concepts lead to emulators for bound and scattering systems that enable fast and accurate calculations using many different model parameter sets. We also point to future extensions and applications of these emulators for nuclear physics, guided by the mature field of model (order) reduction. All examples discussed here and more are available as interactive, open-source Python code so that practitioners can readily adapt projection-based emulators for their own work.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Supplemental Data for the Manuscript: Quantification of Manganese for ChemCam Mars and Laboratory Spectra Using a Multivariate Model

This dataset includes all of the data needed to validate and/or reproduce the manganese calibration model described in the manuscript. The reference database contains metadata for the new Mn-bearing standards, minerals, and mixtures that are > 2.9 wt.% MnO. In addition, the files include the MnO composition data for all standards used, non-normalized spectral data, mean peak area spectrum, results of outlier determination, RMSECV data, regression vectors, and Test Set predictions.

58 GEOSCIENCES↗

DOE OSTI2020

EVALUATION OF PRESSURE DROP CORRELATIONS FOR THE WIRE-WRAPPED ROD BUNDLES

The accurate prediction of pressure drop in the fuel rod bundle is of importance for the design and thermal-hydraulic analysis of nuclear reactor system. Due to very complex geometry of wire-wrapped fuel rod bundle geometry for the Sodium Fast Reactor (SFR), a simple method using hydraulic (equivalent) diameter is not sufficient to predict the pressure drop of rod bundle accurately. For several decades, many experimental works have been performed to develop an accurate correlation for wire-wrapped fuel bundle friction factor. In these works, the friction factor correlation of wire-wrapped fuel bundle has been developed as a function of Reynolds number of the flow and the design parameters such as fuel pin diameter, wire diameter, rod pitch, and wire lead length. The Cheng and Todreas correlations are well-known and used in many subchannel analysis code, such as CADET, TRIO-U, MATRA-LMW, SE2-ANL, etc. Novendstern model, Rehme model, Baxi and Dalle Donne model are also well-known and widely referred. Computational Fluid Dynamics is another typical approach to predict the pressure drop of wire-wrapped fuel rod bundle, but it requires the model validation because the accuracy of pressure drop prediction by the CFD simulation depends on what turbulence model is employed. The present work aims at evaluating the existing pressure drop correlations for the wire-wrapped fuel rod bundle and evaluating the pressure drop of 217-pin rod bundle by the CFD analysis.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2016

On the Modeling of Wall Heat Flux Partitioning in Subcooled Flow Boiling

Accurate prediction of void distribution in reactor coolant channels at subcooled boiling conditions is an important factor in the analysis of the operating conditions of both pressurized water reactors (PWRs) and boiling water reactors (BWRs). Its importance arises from purely thermal-hydraulic considerations (thermal limits, CRUD formation, etc.) and the impact of void reactivity feedback on core neutronics. A mechanistic multidimensional model of subcooled boiling was originally developed by Kurul and Podowski. Whereas this model has been implemented in several commercial CFD codes and successfully used in computer simulations of flow and phase distributions in the coolant channels of light water reactor, additional new modeling aspects of forced-convection subcooled boiling heat transfer have been investigated in recent studies. The purpose of this paper is to formulate a modified model of wall heat flux partitioning, which allows for capturing and quantifying the effect of simultaneous evaporation and condensation at the heated wall on the net evaporation rate and wall temperature. The new model has been implemented in the NPHASE-CMFD code, numerically tested and validated against experimental data. A mechanistic wall heat flux partitioning model for subcooled flow boiling has been presented. This model has been combined with extensively tested models of interfacial mass, momentum and energy transfer terms. It turns out that the model predictions of the wall temperature and void fraction are in good agreement with the experimental data of reference. Future work will focus on the continuation of model validation against experimental data, and on extending its scope to include the phenomena governing departure from nucleate boiling. (authors)

42 ENGINEERING↗

DOE OSTI2015

A Pilot Evaluation of a 4-Dimensional Cone-Beam Computed Tomographic Scheme Based on Simultaneous Motion Estimation and Image Reconstruction

Purpose: To evaluate the performance of a 4-dimensional (4-D) cone-beam computed tomographic (CBCT) reconstruction scheme based on simultaneous motion estimation and image reconstruction (SMEIR) through patient studies. Methods and Materials: The SMEIR algorithm contains 2 alternating steps: (1) motion-compensated CBCT reconstruction using projections from all phases to reconstruct a reference phase 4D-CBCT by explicitly considering the motion models between each different phase and (2) estimation of motion models directly from projections by matching the measured projections to the forward projection of the deformed reference phase 4D-CBCT. Four lung cancer patients were scanned for 4 to 6 minutes to obtain approximately 2000 projections for each patient. To evaluate the performance of the SMEIR algorithm on a conventional 1-minute CBCT scan, the number of projections at each phase was reduced by a factor of 5, 8, or 10 for each patient. Then, 4D-CBCTs were reconstructed from the down-sampled projections using Feldkamp-Davis-Kress, total variation (TV) minimization, prior image constrained compressive sensing (PICCS), and SMEIR. Using the 4D-CBCT reconstructed from the fully sampled projections as a reference, the relative error (RE) of reconstructed images, root mean square error (RMSE), and maximum error (MaxE) of estimated tumor positions were analyzed to quantify the performance of the SMEIR algorithm. Results: The SMEIR algorithm can achieve results consistent with the reference 4D-CBCT reconstructed with many more projections per phase. With an average of 30 to 40 projections per phase, the MaxE in tumor position detection is less than 1 mm in SMEIR for all 4 patients. Conclusion: The results from a limited number of patients show that SMEIR is a promising tool for high-quality 4D-CBCT reconstruction and tumor motion modeling.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2019

Numerical tests of coherence-corrected surface hopping methods using a donor-bridge-acceptor model system

Surface hopping (SH) is a popular mixed quantum-classical method for modeling nonadiabatic excited state processes in molecules and condensed phase materials. The method is simple, efficient, and easy to implement, but the use of classical and independent nuclear trajectories introduces an overcoherence in the electronic density matrix which, if ignored, often leads to spurious results, such as overestimated reaction rates. Several methods have been proposed to incorporate decoherence into SH simulations, but a lack of insightful benchmarks makes their relative accuracy unknown. Herein, we run numerical simulations of common coherence-corrected SH methods including Truhlar’s decay-of-mixing (DOM) and Subotnik’s augmented SH using a Donor-bridge-Acceptor (DbA) model system. Numerical simulations are carried out in the superexchange regime, where charge transfer proceeds from a donor to an acceptor as a result of donor-bridge and bridge-acceptor couplings. The computed donor-to-acceptor reaction rates are compared to the reference Marcus theory results. For the DbA model under consideration, augmented SH recovers Marcus theory with quantitative accuracy, whereas DOM is only qualitatively accurate depending on whether predefined parameters in the decoherence rate are chosen wisely. We propose a general method for parameterizing the decoherence rate in the DOM method, which improves the method’s reaction rates and presumably increases its transferability. Altogether, the decoherence method of choice must be chosen with great care and this work provides insight using an exactly solvable model.

36 MATERIALS SCIENCE↗