Theoretical Chemical Characterization of Energetic Materials
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Theoretical Chemical Characterization of Energetic Materials Betsy M. Rice and Edward F. C. Byrd Ballistics and Weapons Concepts Division Weapons and Materials Research Directorate U. S. Army Research Laboratory Aberdeen Proving Ground, Maryland 21005-5069 ABSTRACT Our research is focused on developing computational capabilities for the prediction of properties of energetic materials associated with performance and sensitivity. Additionally, we want to identify and characterize the dynamic processes that influence conversion of an energetic material to products upon initiation. We are attempting to achieve these goals through the use of standard atomistic simulation methods. In this paper various theoretical chemistry methods and applications to energetic materials will be described. Current capabilities in predicting structures, thermodynamic properties, and dynamic behavior of these materials will be demonstrated. These are presented to exemplify how information generated from atomistic simulations can be used in the design, development, and testing of new energetic materials. In addition to illustrating current capabilities, we will discuss limitations of the methodologies and needs for advancing the state of the art in this area. INTRODUCTION The development of atomistic simulation methods for use in energetic materials (EM) R&D programs has received increasing support within the DOD and DOE for several reasons. The most obvious is the need to optimize the expensive, time-consuming, and often hazardous synthesis, testing, and fielding of a new material. Elimination of poor candidate materials before investing in synthesis and testing will go far toward achieving this goal. The development of computational atomistic methods to predict properties related to performance and sensitivity allow such screening upon the conception of a new material. Significant attention has been given to prediction of two properties that are used to provide an initial assessment of the potential performance of a material in a gun or warhead: the heat of formation and the density of the material. Performance metrics (impetus in a gun, as well as detonation velocities and pressures in a warhead) are dependent on the energy content of the charge, reflected by the heat of formation of the energetic material, and the density, which is an indicator of how much material can be packed into the charge. Therefore, a high-density material with a high heat of formation would appear to be a desirable candidate. Unfortunately, such materials tend to have increased sensitivity to shock, impact, friction, or heat. If the sensitivity is such that the material cannot be handled or will initiate under conditions for which it was not intended, the material is limited in its applications. Therefore, the ability to predict the sensitivity of a material is of equal importantance to prediction of performance properties and has been pursued through a variety of calculation and testing methods [1, 2]. Finally, the negative effects of munitions on
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