Anharmonic effects in the heat capacity of Al

摘要: Mechanical properties of solids are governed by crystal imperfections. Computational materials science is largely concerned with the modelling such defects, e.g. their formation, migration, and interaction energies. Atomistic simulations systems containing lattice defects inherently difficult because generally complicated geometrical structure need for large simulation cells, etc. In this thesis, role in mechanism behind homogeneous melting demonstrated. Also, a generic calculational scheme studying atomic vibrations close to extended (applied dislocation) has been considered. Furthermore, heat capacities solid liquid phases aluminium have calculated, as well various thermophysical defect properties. The work was carried out using classical atomistic simulations, mainly molecular dynamics, copper. interatomic forces were modelled effective interactions embedded-atom type. main results thesis following: • thermal fluctuation initiating an aggregate typically 6-7 interstitials 3-4 vacancies. initial stage melting, no signs shear modulus mechanism, or presence line-like (dislocations), can be seen. typical time interval from when initiates at which phase fully developed order 1000τ, where period τ corresponds maximum vibrational frequency solid. solid-liquid boundary advances pace comparable that transport vibrating atoms high temperatures. seemingly small anharmonic effect capacity caused partial cancellation low-order term linear temperature terms higher temperature. core region edge dislocation face-centred cubic compressed expanded regions. excess volume associated small, about 6 percent volume, result between changes regions give negative positive contributions, respectively, entropy. overall entropy 2kB per repeat length along core. near considering cluster 500-1000 dislocation, embedded discrete, but relaxed, 23 000 atoms. An four layers thick 18 diameters long direction parallel Burgers vector, accounts most constant-pressure shows minimum function phase.