@article{ponciroli_shriwise_mei_stauff_petersen_romano_2022, title={Simulation-based methodology to assess the lattice defects creation as energy storing process}, volume={165}, ISSN={["1873-2100"]}, DOI={10.1016/j.anucene.2021.108691}, abstractNote={In nuclear industry, damages caused to in-core structural materials by high-energy neutrons have been studied for years. Recently, the possibility of storing energy through the creation of defects in crystalline materials via heavy particle bombardment was investigated. To evaluate the potential of the Wigner effect as energy-storing process, a graphite-moderated Molten Salt Reactor was adopted as a test case. Neutronics simulations performed with OpenMC Monte Carlo code allowed estimating the amount of energy released during fission events, the fraction that is deposited in graphite, and the fraction that has the potential to cause radiation damages. Molecular dynamics simulations were then performed to study the evolution of cascades triggered by high-energy neutrons. As a major outcome, a more accurate estimate of the radiation damage with respect to the traditional approaches was obtained, and the fraction of the deposited neutron energy that can be stored through long-lived defects was quantified.}, journal={ANNALS OF NUCLEAR ENERGY}, author={Ponciroli, Roberto and Shriwise, Patrick and Mei, Zhi-Gang and Stauff, Nicolas and Petersen, Andrew and Romano, Paul}, year={2022}, month={Jan} }
 @article{mei_ponciroli_petersen_2022, title={Wigner energy in irradiated graphite: A first-principles study}, volume={563}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2022.153663}, abstractNote={First-principles calculations were performed to examine the defect-induced energy storage in graphite. The accumulation of energy resulting from inducing defects in graphite is a well-known phenomenon. Given the recent interest in exploiting this process for energy-storing purposes, more careful investigation is necessary. Some of the earliest studies of damaged graphite, and the stored energy associated with that, were motivated by the associated technological issues in nuclear reactor operation. A large number of excited state defects, for example Frenkel pairs, can be generated in graphite through bombardment of high-energy neutrons. The sudden release of this energy (also called Wigner energy) poses a serious concern to the safe operation of nuclear reactors. At the same time, controlled defect generation in graphite using neutron/ion irradiation might represent a potential energy storage mechanism. In recently published papers, the design of an integrated energy system that couples a nuclear reactor with a Wigner effect-based energy storing system was proposed. To accurately estimate the performance that can be achieved in terms of stored energy density through defect generation, density functional theory (DFT) based first-principles calculations were performed. In this work, stored energy accumulation was modeled in two ways - by Frenkel pair accumulation and overlapping collision cascade methods. The former was done with ab initio molecular dynamics (AIMD) simulations, and the latter was done with combined classical molecular dynamics (MD) and AIMD simulations. The agreement between the calculated and experimental results for how stored energy changes with dosage suggests that this model could be useful for the on-going research into damaged graphite as an energy storage medium.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Mei, Zhi-Gang and Ponciroli, R. and Petersen, A.}, year={2022}, month={May} }
 @article{adhikari_mostofian_copperman_subramanian_petersen_zuckerman_2019, title={Computational Estimation of Microsecond to Second Atomistic Folding Times}, volume={141}, ISSN={["1520-5126"]}, DOI={10.1021/jacs.8b10735}, abstractNote={Despite the development of massively parallel computing hardware including inexpensive graphics processing units (GPUs), it has remained infeasible to simulate the folding of atomistic proteins at room temperature using conventional molecular dynamics (MD) beyond the microsecond scale. Here, we report the folding of atomistic, implicitly solvated protein systems with folding times τ ranging from ∼10 μs to ∼100 ms using the weighted ensemble (WE) strategy in combination with GPU computing. Starting from an initial structure or set of structures, WE organizes an ensemble of GPU-accelerated MD trajectory segments via intermittent pruning and replication events to generate statistically unbiased estimates of rate constants for rare events such as folding; no biasing forces are used. Although the variance among atomistic WE folding runs is significant, multiple independent runs are used to reduce and quantify statistical uncertainty. Folding times are estimated directly from WE probability flux and from history-augmented Markov analysis of the WE data. Three systems were examined: NTL9 at low solvent viscosity (yielding τf = 0.8-9 μs), NTL9 at water-like viscosity (τf = 0.2-2 ms), and Protein G at low viscosity (τf = 3-200 ms). In all cases, the folding time, uncertainty, and ensemble properties could be estimated from WE simulation; for Protein G, this characterization required significantly less overall computing than would be required to observe a single folding event with conventional MD simulations. Our results suggest that the use and calibration of force fields and solvent models for precise estimation of kinetic quantities is becoming feasible.}, number={16}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Adhikari, Upendra and Mostofian, Barmak and Copperman, Jeremy and Subramanian, Sundar Raman and Petersen, Andrew A. and Zuckerman, Daniel M.}, year={2019}, month={Apr}, pages={6519–6526} }
 @article{petersen_gillette_2018, title={High-temperature annealing of graphite: A molecular dynamics study}, volume={503}, ISSN={["1873-4820"]}, DOI={10.1016/j.jnucmat.2018.03.011}, abstractNote={A modified AIREBO potential was developed to simulate the effects of thermal annealing on the structure and physical properties of damaged graphite. AIREBO parameter modifications were made to reproduce Density Functional Theory interstitial results. These changes to the potential resulted in high-temperature annealing of the model, as measured by stored-energy reduction. These results show some resemblance to experimental high-temperature annealing results, and show promise that annealing effects in graphite are accessible with molecular dynamics and reactive potentials.}, journal={JOURNAL OF NUCLEAR MATERIALS}, author={Petersen, Andrew and Gillette, Victor}, year={2018}, month={May}, pages={157–163} }