@article{mei_mohamed_eapen_2018, title={Approach to local thermodynamic equilibrium and the evolution to a glassy core following neutron/ion radiation impact}, volume={98}, ISSN={["1478-6443"]}, DOI={10.1080/14786435.2018.1502482}, abstractNote={ABSTRACT Using molecular dynamics simulations and statistical-mechanical metrics, we make quantitative predictions on the local thermodynamic and dynamic states following an ion or neutron impact in three materials – copper, silicon and solid argon. Through a two-energy distribution, we first capture the non-equilibrium temperature evolution and the approach to the local thermal equilibrium in three generic stages. By examining the time-resolved van Hove self-correlator, we then demonstrate that the impact core of all the three materials shows the dynamic characteristics of a jammed or glassy state. We delineate a dynamic atom-hopping mechanism that attests to a rapid defect recovery stage in copper; silicon, on the contrary, accommodates only small displacements which resist recovery. The dissimilitude between copper with a close-packed structure and silicon with an open network structure is further drawn out through an isoconfigurational analysis of displacements, which shows a compact dendritic-like condensation front for the mobile atoms in copper through atom hopping. In contrast, silicon portrays larger-scale spatial oscillations of dynamically separated regions, which appear to be a precursor to dynamic lattice instability and eventual amorphisation.}, number={29}, journal={PHILOSOPHICAL MAGAZINE}, author={Mei, Xiaojun and Mohamed, Walid and Eapen, Jacob}, year={2018}, pages={2701–2722} }
 @article{annamareddy_nandi_mei_eapen_2014, title={Waxing and waning of dynamical heterogeneity in the superionic state}, volume={89}, ISSN={["1550-2376"]}, DOI={10.1103/physreve.89.010301}, abstractNote={Using molecular dynamics simulations of UO2-a type II superionic conductor-we identify a well-defined onset of dynamic disorder (Tα), which is remarkably correlated to a nontrivial advance of dynamical heterogeneity (DH). Quantified by the correlations in the dynamic propensity and van Hove self-correlation function, the DH is shown to grow with increasing temperature from Tα, peak at an intermediate temperature between Tα and Tλ-the superionic transition temperature-and then recede. Surprisingly, the DH attributes are not uniform across the temperatures-our investigation shows a low temperature (αT) stage DH, which is characterized by weak correlations and a plateaulike period in the correlations of the propensity, and a high temperature (λT) stage DH with strong correlations that are analogous to those in typical supercooled liquids. Our work, which has rigorously identified the onset of superionicity, gives a different direction for interpreting scattering experiments on the basis of statistical, correlated dynamics.}, number={1}, journal={PHYSICAL REVIEW E}, author={Annamareddy, V. Ajay and Nandi, Prithwish K. and Mei, Xiaojun and Eapen, Jacob}, year={2014}, month={Jan} }
 @article{mei_eapen_2013, title={Dynamic transitions in molecular dynamics simulations of supercooled silicon}, volume={87}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.87.134206}, abstractNote={Two dynamic transitions or crossovers, one at a low temperature (T∗ ≈ 1006 K) and the other at a high temperature (T0 ≈ 1384 K), are shown to emerge in supercooled liquid silicon using molecular dynamics simulations. The high-temperature transition (T0) marks the decoupling of stress, density, and energy relaxation mechanisms. At the low-temperature transition (T∗), depending on the cooling rate, supercooled silicon can either undergo a high-density-liquid to low-density-liquid (HDL-LDL) phase transition or experience an HDL-HDL crossover. Dynamically heterogeneous domains that emerge with supercooling become prominent across the HDL-HDL transition at 1006 K, with well-separated mobile and immobile regions. Interestingly, across the HDL-LDL transition, the most mobile atoms form large prominent aggregates while the least mobile atoms get spatially dispersed akin to that in a crystalline state. The attendant partial return to spatial uniformity with the HDL-LDL phase transition indicates a dynamic mechanism for relieving the frustration in supercooled states.}, number={13}, journal={PHYSICAL REVIEW B}, author={Mei, Xiaojun and Eapen, Jacob}, year={2013}, month={Apr} }