Quantum-based atomisticsimulation of materials properties in transition metals

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We present an overview of recent work on quantum-based atomisticsimulation of materials properties in transition metalsperformed in the Metals and Alloys Group at Lawrence LivermoreNational Laboratory. Central to much of this effort has beenthe development, from fundamental quantum mechanics, of robustmany-body interatomic potentials for bcc transition metals viamodel generalized pseudopotential theory (MGPT), providing closelinkage between ab initio electronic-structurecalculations and large-scale static and dynamic atomisticsimulations. In the case of tantalum (Ta), accurate MGPTpotentials have been so obtained that are applicable tostructural, thermodynamic, defect, and mechanical propertiesover wide ranges of pressure and temperature. Successfulapplication areas discussed include structural phase stability,equation of state, melting, rapid resolidification,high-pressure elastic moduli, ideal shear strength, vacancy andself-interstitial formation and migration, grain-boundary atomicstructure, and dislocation core structure and mobility. Anumber of the simulated properties allow detailed validation ofthe Ta potentials through comparisons with experiment and/orparallel electronic-structure calculations. Elastic anddislocation properties provide direct input intohigher-length-scale multiscale simulations of plasticity andstrength. Corresponding effort has also been initiated on themultiscale materials modelling of fracture and failure. Herelarge-scale atomistic simulations and novel real-time characterization techniques are being used to study voidnucleation, growth, interaction, and coalescence in series-endfcc transition metals. We have so investigated the microscopicmechanisms of void nucleation in polycrystalline copper (Cu),and void growth in single-crystal and polycrystalline Cu,undergoing triaxial expansion at a large, constant strain rate - aprocess central to the initial phase of dynamic fracture. The influence of pre-existing microstructure on the void growthhas been characterized both for nucleation and for growth, andthese processes are found to be in agreement with the generalfeatures of void distributions observed in experiment. We havealso examined some of the microscopic mechanisms of plasticityassociated with void growth.