Development And Application Of EAM Empirical Potentials For Some Metals And Alloys

The atomic interactions play an important role in determining the physical properties of metals or alloys.The empirical potentials describing the atomic interactions should be known before the performance of classical simulations,for example,molecular dynamic(MD)or Monte Carlo(MC)simulations.For a large number of metals and alloys,the limitations of the available empirical potentials considerably restrict their applications in amounts of simulations.Therefore,developing precise empirical potentials is an important project in computational material science.In 1980s,Daw and Baskes proposed the original embedded-atom method(EAM)empirical potential for metals and alloys.The simulation results of metals and alloys using EAM potentials,which include the electron density contribution to the embedded energy and multi-body effect among atoms compared with pair potential,agree well with experimental results,and then the EAM potentials are widely used in classical simulations.In this dissertation,we develop the EAM potentials for some typical metals and alloy.Firstly,we develop Gupta potential for some metals.In ambient conditions,alkaline earth metals calcium(Ca),strontium(Sr)and rare earth metals ?-phase lanthanum(?-La)and?-phase cerium(?-Ce)are all face-centered cubic(fcc)metals.We choose and develop Gupta potential,which is suitable for fcc phase solid.The Gupta potential parameters are fitted to experimental lattice constant,cohesive energy and elastic constants.Using the Gupta potential,we calculate the bulk modulus,shear modulus,sound speed,Debye temperature,phonon dispersions,the formation energy of monovacancy,equation of states(EOS)and radial distribution function of liquid,and they agree well with experimental or DFT results.Secondly,we develop Sutton-Chen potential for transition metal iron(Fe).Considering the long-range interactions between atoms at high pressure and temperature,we choose and develop Sutton-Chen potential,which includes long-range interactions.The first-principles MD simulations with 1024 atoms show that at the pressure-temperature(P-T)conditions of the Earth's inner core,bcc phase of iron is dynamically and thermodynamically stable.Further research about the simulation size and duration time effect on the stability of bcc phase can't be realized by first-principles MD method.Then we develop empirical Sutton-Chen potential for iron.The Sutton-Chen potential parameters are fitted to the configuration energy from first-principles MD simulations.It is then applied in the classical MD simulations to explore the simulation size(up to 65536 atoms)and duration time(up to 200 ps)effect on the simulation results.The results from classical MD simulations are consistent with that from first-principles MD simulations,at the P-T conditions of the Earth's inner core bcc phase of iron is dynamically and thermodynamically stable.The calculation results of vibration entropy and phonon density of state(PDOS)also support the conclusion.Finally,we develop improved Finnis-Sinclair(IFS)potential for vanadium-rich ternary vanadium-titanium-chromium(V-Ti-Cr)alloy.In ambient conditions,the V-rich alloys are body-centered cubic(bcc)structures,so we chose IFS potential,which is suitable for bcc phase.The potential parameters are fitted to experimental or DFT structure parameters,cohesive energy,and elastic constants.Using the IFS potential,we can reproduce these values very well.The formation energy of monovacancy and interstitial atom of pure V agree well with the available experimental data or DFT data.Therefore,we use the IFS potential to study the mechanical properties and defect properties of typical V-4Ti-4Cr alloy.The bulk modulus and shear modulus are in line with experimental data,and vacancy formation energies of different sites(V,Ti and Cr)also agree well with DFT data.