A bond-order potential for atomistic simulations in iron

摘要

A new semi-empirical potential for Fe based onthe quantum chemistry concept of bond order has beendeveloped. The potential consists of two parts: the repulsiveshort-range exponential potential, and the attractive potential,also of the exponential form, with a bond-order prefactor. Thelatter depends on angles between the Fe-Fe bonds, and uses theenvironmental parameter similar to that of the Tersoff bond-order potential for tetrahedrally bonded semiconductors. Thebond order function (depending on the above environmentalparameter), however, is of a more general form than that of theTersoff potential. The new potential was calibrated using thetraditional fitting to the Universal Scaling and the equilibriumvolume and cohesive energy of BCC Fe. The introduced'punishment functions' also directed the multi-variateminimization process towards minimizing the deviationsbetween the calculated and experimental values of the elasticmoduli C' and C_(44), the energies of FCC and HCP Femodifications, and the (111) free surface energy. With the totalof 15 fitted parameters, the potential reproduces with only minordeviations the elastic moduli, the volume-pressure equation ofstates in BCC phase, the energies in FCC and HCPmodifications, the BCC-HCP phase transformation underpressure. and the energy of the (111) free surface. Other tests ofthe new potential are being currently performed. The potentialwill be used in atomistic simulations of lattice stability, anddeformation and chemisorption processes in Fe.