Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.

Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult CO double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO2 conversion and utilization. Here, we discuss in detail the approaches of CO2 conversion, the developmental history, the basic principles, the economic feasibility of CO2/H2O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

A review of high temperature co-electrolysis of H2O and CO2 to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology

The electrocatalytic reduction of CO2 into value-added chemicals such as hydrocarbons has the potential for supplying fuel energy and reducing environmental hazards, while the accurate tuning of electrocatalysts at the ultimate single-atomic level remains extremely challenging. In this work, we demonstrate an atomic design of multiple oxygen vacancy-bound, single-atomic Cu-substituted CeO2 to optimize the CO2 electrocatalytic reduction to CH4. We carried out theoretical calculations to predict that the single-atomic Cu substitution in CeO2(110) surface can stably enrich up to three oxygen vacancies around each Cu site, yielding a highly effective catalytic center for CO2 adsorption and activation. This theoretical prediction is consistent with our controlled synthesis of the Cu-doped, mesoporous CeO2 nanorods. Structural characterizations indicate that the low concentration (<5%) Cu species in CeO2 nanorods are highly dispersed at single-atomic level with an unconventionally low coordination number ∼5, su...

Single-Atomic Cu with Multiple Oxygen Vacancies on Ceria for Electrocatalytic CO2 Reduction to CH4

Defect and Interface Engineering for Aqueous Electrocatalytic CO2 Reduction

Solvent effects in the hydrogenation of 2-butanone

Density functional theory (DFT) calculations were performed to study the mechanism of carbon dioxide (CO2) reduction to carbon monoxide (CO) and methanol (CH3OH) on CeO2(110) surface. CO2 dissociates to CO on interacting with the oxygen vacancy on reduced ceria surface. The oxygen atom heals the vacancy site and regenerates the stoichiometric surface via a redox mechanism with intrinsic activation and reaction energies of 259.2 and 238.6 kJ/mol, respectively. Lateral interaction of oxygen vacancies were studied by the generation of two oxygen vacancies per unit of CeO2 surface. Compared to a single isolated vacancy, the activation and reaction energies of CO2 dissociation on a divacancy were approximately reduced to half of its value. Hydrogen atom coadsorbed on the surface was observed to assist CO2 dissociation by forming a carboxyl intermediate, CO2+H → COOH (ΔEact = 39.0 kJ/mol, ΔH = −69.2 kJ/mol) which on subsequent dissociation produces CO via the redox mechanism. On hydrogenation, CO is likely to p...

Nishant Sinha

Papers

Solvent effects in the hydrogenation of 2-butanone

Role of Reduced CeO2(110) Surface for CO2 Reduction to CO and Methanol

Molecular modeling studies of oleate adsorption on iron oxides

Ionic liquids as novel quartz collectors: Insights from experiments and theory

CO2 Reduction to Methanol on CeO2 (110) Surface: a Density Functional Theory Study