Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of spins.Alternatively,we discuss how to semiclassically approach the qua...Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of spins.Alternatively,we discuss how to semiclassically approach the quantum problem and demonstrate a simple method for introducing a locally approximate form of spin quantization.While the procedure underestimates magnetic short-range order,our results suggest a simple correction for recovering realistic spin–spin correlations above the critical temperature.Moreover,ensemble fluctuations are found to provide reasonably accurate thermodynamics,largely reproducing quantum mechanically calculated heat capacities and experimental magnetometry for ferromagnetic Fe and antiferromagnetic RbMnF3.Extensions of the method are proposed to address remaining inaccuracies.展开更多
The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations,contrasting behavior in elemental Nb with that in brittle NbMo...The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations,contrasting behavior in elemental Nb with that in brittle NbMoTaW and ductile Nb_(45)Ta_(25)Ti_(15)Hf_(15).We employ machine-learning interatomic potentials(MLIPs),including a new MLIP developed for NbTaTiHf,in atomistic simulations of crack tip extension mechanisms based on analyses of atomistic fracture resistance curves.While the initial behavior of sharp cracks shows good correspondence with the Rice theory,fracture resistance curves reveal marked changes in fracture modes for the complex alloys as crack extension proceeds.In NbMoTaW,compositional complexity appears to promote dislocation nucleation relative to pure Nb,despite theoretical predictions that the alloy should be relatively more brittle.In Nb_(45)Ta_(25)Ti_(15)Hf_(15),alloying alters the fracture mode compared to elemental Nb,promoting crack tip blunting and enhancing resistance to crack propagation.展开更多
基金F.W.was supported by the U.S.Department of Defense through the National Defense Science and Engineering Graduate Fellowship ProgramM.A.and L.-W.W.were supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division,under Contract No.DE-AC02-05-CH11231(Materials Project program KC23MP and Non-Equilibrium Magnetic Materials program MSMAG,respectively)Computational resources were provided by award BES-ERCAP0021088 of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility at Lawrence Berkeley National Laboratory,operated under the same contract.
文摘Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of spins.Alternatively,we discuss how to semiclassically approach the quantum problem and demonstrate a simple method for introducing a locally approximate form of spin quantization.While the procedure underestimates magnetic short-range order,our results suggest a simple correction for recovering realistic spin–spin correlations above the critical temperature.Moreover,ensemble fluctuations are found to provide reasonably accurate thermodynamics,largely reproducing quantum mechanically calculated heat capacities and experimental magnetometry for ferromagnetic Fe and antiferromagnetic RbMnF3.Extensions of the method are proposed to address remaining inaccuracies.
基金supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division,under Contract No.DE-AC02-05-CH11231 within the Damage Tolerance in Structural Materials(KC 13)programThe study made use of resources of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory,operated under the same contract number,using NERSC Award No.BES-ERCAP0027535This research used the Lawrencium computational cluster resource provided by the IT Division at the Lawrence Berkeley National Laboratory(Supported by the Director,Office of Science,Office of Basic Energy Sciences,of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231).The Scientific Computing Group(also known as High-Performance Computing Services)under Science IT supports the mission of Lawrence Berkeley National Laboratory by providing technology and consulting support for science and technical programs,in the areas of data management,HPC cluster computing,and Cloud services.
文摘The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations,contrasting behavior in elemental Nb with that in brittle NbMoTaW and ductile Nb_(45)Ta_(25)Ti_(15)Hf_(15).We employ machine-learning interatomic potentials(MLIPs),including a new MLIP developed for NbTaTiHf,in atomistic simulations of crack tip extension mechanisms based on analyses of atomistic fracture resistance curves.While the initial behavior of sharp cracks shows good correspondence with the Rice theory,fracture resistance curves reveal marked changes in fracture modes for the complex alloys as crack extension proceeds.In NbMoTaW,compositional complexity appears to promote dislocation nucleation relative to pure Nb,despite theoretical predictions that the alloy should be relatively more brittle.In Nb_(45)Ta_(25)Ti_(15)Hf_(15),alloying alters the fracture mode compared to elemental Nb,promoting crack tip blunting and enhancing resistance to crack propagation.
