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Session I27 - Materials Theory - Simulations IV Defects and Fracture.
MIXED session, Wednesday morning, March 20
Room 127, America's Center
Using multi-ion interatomic potentials derived from first-principles generalized pseudopotential theory, we are studying point defects and dislocations in molybdenum (Mo). For point defects, the calculated vacancy formation and activation energies are in excellent agreement with experimental results. In ascending order, the sequence of energetically stable self- interstitials is: <110> split dumb-bell, tetrahedral site, crowdion, <111> split dumb-bell, <100> split dumb-bell, and octahedral site. In addition, the migration paths for the <110> dumb-bell interstitial have been studied. The migration energy is found to be one order of magnitude higher than previous theoretical estimates obtained using a Finnis-Sinclair potential for Mo. The energetics and core structure of <111> screw dislocations in Mo are being investigated. We have found that the ``easy" core configuration has lower formation energy than the ``hard" one, consistent with previous theoretical studies. The differential displacement method has been used to elaborate the details of both dislocation configurations, revealing some new and interesting features. Calculation of the Peierls barrier is in progress and extention of the work to tantalum (Ta) is planned.