2019年-MaterialMigrationandMaterialMiingmeeting-EFDAPWITask材料的迁移与材料混合会议-EFDA

1、HELSINGIN YLIOPISTO HELSINGFORS UNIVERSITETUNIVERSITY OF HELSINKIDevelopment of analytical bondorder potentials for the Be-C-W-H systemC BiBrkas, N. Juslin, K. Vortler, H. Timko, K. NordlundDepartment of Physics, University of HelsinkiK HenrikssonDepartment of Chemistry, University of HelsinkiP. Erh

2、artLawrenee Livermore National Laboratory, Livermore, USAJoint TFESEWG Material Migration and Material Mixing meeting We all want to understand what is going on in a fusion reactor Erosion, redeposition, formation of mixed materials, . Ideally we would be able to test every possible situation that c

3、ould occur But, experiments are timely and difficult The interesting phenomena take place at the atomlevel and at very small time scales Hence, they are hardly accessible to experiments Therefore Molecular Dynamics (MD) can be used60 millionstime v 1 ns100 nmMD Approximati ons: Atoms treated as obje

4、cts with no internal structure No electronic structure calculations done-May include electronic stopping and electron phonon coupling as frictionE.g. 41 106 atoms, 72 x 72 x 72 nm, 35 ps, 1024 processors = 36 hMD algorithm Only with a reliable interatomic potential can we model things correctly A po

5、tential must at least be able to reproduce: Ground state properties and non-equilibrium processes such as different phases, melting point, defect structures and energetics, . Otherwise we don't know what will happen: To model plasma-wall interactions, we need potentials for the Be-C-W-H system W

6、-W, W-H, C-C and H-C made earlier(Brenner PRB 42 (1990) 9458 and Juslin efa/. JAP 98 (2019) 123520 Now we develop Be-C, Be-Be, Be-H and Be-W Many different forms of potentials exist Simple pair potentials, EAM, MEAM, BOP We chose the BOF formalism It is based on Linus Pauling's bond order concep

7、t It can describe: The angular dependency of covalent bonds Breaking of bonds It has successfully been applied to many systems e.g. Si, C, SiC, W, Pt, Zn, ZnO, GaAs, GaN, Fe,.Bond Order = the strength of the bond between two atoms depends on the surroundings of the bondIBOPexp.IEgh3.32 eV-3.32 eVa2.

8、3 A2.29 Ac/a1.571.57B120 Gpa116.8 GpaTpnelt1550±50 K1560 Kav38.2 1 O'61/K29.0 1 O'61/K Be has hep as ground phase bcc and fee may also exist Potential vs. experimentsZ= 12Be Pauling plot(puoq><D) Im 60_InterstitialsBOPDFT IDFT ll|BT (eV)1.220.81.58O(eV)1.46unstable1.79Ground state

9、 仃)(eV)1.040.81.58BT toO0.430.38MoleculesBOPDFTmigration barrier (eV)Be-H341.3.34EeV)Be-H3 D3hEeV)I S)-1.651.35-1.311.41-2.131.33-1.351.47 The Be-H potential was fitted to molecules and H defects in Be Almost the right ground state interstitial H in Be Most of Be-H. molecules ok D and T are also mod

10、ellable with this potential?ting Be-C poorly known experimentally Only one phase observed, the ionic antifluorite Be2C Potential vs. experimentsBOPexp.IEgh5.34 eV5.4 一 -5.85 eVa4.57 A4.34 AB227 Gpa> 233 GpaTfnelt3150±50K2670 Kav4.5 10'61/K5.8 10'61/Kixing meeting300002500020000150001

11、00005000 We ensured that there are no false minima Cooled a random melt (Be:C = 2:1) to zero K The atoms crystallized into the antifluorite structure The correct Be2C really is the ground structure of the potential36384.042-4.4-4.6-4.850-5.241.01.21.41.61.82.02.22.42.62.8radial di st a nee (A)Comple

12、x phase diagram: Be2W, Be12W, Be22W seenH. Okamoto and L.E. Tarn审，1986. Initial test of the Be2W phase: What becomes of the ideal hexagonal Laves structure?DFT: Ecoh = -7.03 eV/ata = 4.46 ABOP: Ecoh = -6.72 eV/at a = 4.70 A c/a = 1.60Self sputtering 20 - 100 eV Be ion irradiation flux 2 1028 m-2s_1, room T Sput. threshold 20 一 50 eV Yield agrees with extrapolated exp.Be does not amorphize<>» At 1500 KC irradiation of Be Layers of Be2C are formed close to the initial Be surface Sputtering threshold 20 - 5