RESUMEN
Searching for advanced strategies to alleviate the inherent contradiction between stability and performance has been one of the most challenging tasks in the development of high-energy-density materials (HEDMs) for centuries. Recently, our high-throughput calculations and machine learning studies showed that cage-like HEDMs have a high probability of owning simultaneous high thermostability and high performance. To explore the physical mechanism of the data-driven prediction, quantum mechanical molecular dynamics simulations were carried out to study the early thermolysis of a series of caged HEDMs at the crystal level. Herein, an interesting competitive process between backbone-collapse and branch-heterolysis was discovered, and the process was found to significantly relate to the temperature and isotropy degree of the cage-like conformation. In the simulated storage or transport temperature range, branch-heterolysis is the predominating process. The highly isotropic cage-like conformation can delay the onset time of HEDMs, providing the reactant molecules with extra stability to suppress successive decomposition. However, in the simulated explosion temperature range, the backbone-collapse became dominant. A considerable scope of reactant molecules was initiated through backbone-collapse, which deteriorated the thermostability of the caged HEDMs and accelerated their energy release, endowing them with higher performance. The current research demonstrates cage-like conformations in alleviating the stability-performance contradiction of HEDMs and provides a theoretical guide for the rational design of novel advanced compounds.
RESUMEN
To accelerate the groundwater flow simulation process, this paper reports our work on developing an efficient parallel simulator through rebuilding the well-known software MODFLOW on JASMIN (J Adaptive Structured Meshes applications Infrastructure). The rebuilding process is achieved by designing patch-based data structure and parallel algorithms as well as adding slight modifications to the compute flow and subroutines in MODFLOW. Both the memory requirements and computing efforts are distributed among all processors; and to reduce communication cost, data transfers are batched and conveniently handled by adding ghost nodes to each patch. To further improve performance, constant-head/inactive cells are tagged and neglected during the linear solving process and an efficient load balancing strategy is presented. The accuracy and efficiency are demonstrated through modeling three scenarios: The first application is a field flow problem located at Yanming Lake in China to help design reasonable quantity of groundwater exploitation. Desirable numerical accuracy and significant performance enhancement are obtained. Typically, the tagged program with load balancing strategy running on 40 cores is six times faster than the fastest MICCG-based MODFLOW program. The second test is simulating flow in a highly heterogeneous aquifer. The AMG-based JASMIN program running on 40 cores is nine times faster than the GMG-based MODFLOW program. The third test is a simplified transient flow problem with the order of tens of millions of cells to examine the scalability. Compared to 32 cores, parallel efficiency of 77 and 68% are obtained on 512 and 1024 cores, respectively, which indicates impressive scalability.