Accurate Energy Evaluation Research Articles

PyGACE: Combining the genetic algorithm and cluster expansion methods to predict the ground-state structure of systems containing point defects

Searching the most stable atomic-structure of a solid with point defects (including the extrinsic alloying/doping elements), is one of the central issues in materials science. Both adequate sampling of the configuration space and the accurate energy evaluation at relatively low cost are demanding for the structure prediction. In this work, we have employed a framework combining genetic algorithm, cluster expansion (CE) method and first-principles calculations, which can effectively locate the ground-state or meta-stable states of the relatively large/complex systems. We employ this framework to search the stable structures of two distinct systems, i.e., oxygen-vacancy-containing HfO2−x and the Nb-doped SrTi1−xNbxO3, and more stable structures are found compared with the structures available in the literature. The present framework can be applied to the ground-state search of extensive alloyed/doped materials, which is particularly significant for the design of advanced engineering alloys and semiconductors.

Energy and economic assessments of bio-energy systems based on annual and perennial crops for temperate and tropical areas

Bio-energy systems based on dedicated crops depend on efficient and economic feedstock production as a pre-requisite for sustainable development. In this study, 15 annual and perennial species suited for temperate or tropical areas were assessed in terms of energy and financial balance: oil and coconut palm, jatropha, castor bean, sunflower and rapeseed (biodiesel); sugar cane, maize and wheat (1st generation ethanol); poplar, cardoon, giant reed, miscanthus, switchgrass and fibre sorghum (heat and power, or 2nd generation ethanol). Net energy and energy efficiency as respective difference and ratio between produced and consumed energy, and net profit (revenues minus costs) were appraised under temperate or tropical conditions, depending on crop species. In addition, a sensitivity analysis was run to rate the use of oil and grain crop residues as additional energy sources. Net energy, energy efficiency and net profit exhibited a wide range ranged between 22 and 340 GJ ha−1, 2.2 and 21.1 GJ GJ−1, 38 and 415 € ha−1, respectively. Energy sector (biodiesel < 1st generation ethanol < biomass crops) and plant habit (annual < perennial species) were the two main drivers of these large differences. The complementary use of crop residues enhanced net energy (+202%) and energy efficiency (+71%), whereas net profit decreased, as average (−24%), because of higher costs (residue recovery and additional fertilizer doses) than financial returns. It is concluded that accurate evaluation of energy and economic trade-off should be the driver of crop choice and management in energy initiatives involving dedicated crop cultivation.

Research on Additional Specific Consumption Distribution of Biomass Direct Combustion Power Plant

Biomass direct combustion power generation is the most simple but effective way in dealing with environmental issues and energy crisis. A comprehensive diagnosis with accurate evaluation of energy saving potential of a given biomass power plant is of great importance in lowing the cost of generating electricity, reducing the consumption of energy and pollutant emissions [1]. This paper throws light upon an innovative energy consumption diagnosis method-the specific consumption analysis theory, which is based on the First and Second law of thermodynamics [2,3]. Taking a given biomass power plant of National Energy Group as an example, mathematical models are made based on all the components and processes. The specific consumption analysis theory is employed to calculate the specific consumption within the biomass power plant using design parameters under design operating conditions, thus demonstrating the specific consumption distribution in the power plant, which provides theoretical basis for energy-saving and optimization in biomass power plant.

Solving the equations of motion for mixed atomistic and coarse-grained systems

A mixed-resolution molecular dynamics technique is presented that permits simulation of large and complex systems that critically depend on a subtle interplay between energy and entropy and, therefore, require both an accurate energy evaluation and an extensive sampling of a large and complex phase space. The computational approach is based upon the idea that many complex systems can be spatially divided into a relatively small active zone (that requires an accurate energy evaluation but, due to its relatively small size, only a limited sampling of phase space) and a relatively large inactive zone (that requires a less accurate energy description but the sampling of a very large phase space). Mixed-resolution models that use an accurate atomistic model for the active zone and an efficient coarse-grained model (that lumps groups of atoms into pseudo-atoms) for the inactive zone are ideally suited for these systems. One challenge in mixed-resolution simulations is creating a seamless connection between low- and high-resolution zones that exchange groups of atoms. We derive a mixed-resolution Hamiltonian and present a microcanonical simulation protocol that conserves energy and momentum and allows for a change in resolution of selected groups of atoms during a simulation. The method is applicable to simulations in other ensembles and for systems with multiple high-resolution zones. To illustrate the numerical stability of our technique, we present simulation results for a system of mixed-resolution methane molecules.