Change search
ReferencesLink to record
Permanent link

Direct link
Homogeneous melting of superheated crystals: Molecular dynamics simulations
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theory of Materials.
2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 5, 054107- p.Article in journal (Refereed) Published
Abstract [en]

The homogeneous melting mechanism in a superheated fcc lattice is studied through molecular dynamics simulations, usually for about 20 000 atoms, with the Ercolessi and Adams interaction that represents aluminum. The periodic boundary conditions for the simulation cell suppress the usual surface-initiated melting at T-m=939 K, and the solid-to-liquid transition takes place at the temperature T-s=1.3T(m). By logging the position of each atom at every time step in the simulation, we can follow the melting process in detail at the atomic level. Thermal fluctuations close to T-s create interstitial-vacancy pairs, which occasionally separate into mobile interstitials and almost immobile vacancies. There is an attraction between two interstitials, with a calculated maximum interaction energy of about 0.7 eV. When three to four migrating interstitials have come close enough to form a bound aggregate of point defects, and a few thermally created interstitial-vacancy pairs have been added to the aggregate, such a defect configuration usually continues to grow irreversibly to the liquid state. For 20 000 atoms in the simulation cell, the growth process takes about 10(2)tau to be completed, where tau is the period of a typical atomic vibration in the solid phase. This melting mechanism involves fewer atoms in its crucial initial phase than has been suggested in other melting models. The elastic shear moduli c(44) and c(')=(c(11)-c(12))/2 were calculated as a function of temperature and were shown to be finite at the onset of melting.

Place, publisher, year, edition, pages
2005. Vol. 72, no 5, 054107- p.
Keyword [en]
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-25208DOI: 10.1103/PhysRevB.72.054107ISI: 000231564300044ScopusID: 2-s2.0-33644955479OAI: diva2:356478
QC 20101012Available from: 2010-10-12 Created: 2010-10-12 Last updated: 2010-10-13Bibliographically approved
In thesis
1. Atomistic simulations of lattice defects
Open this publication in new window or tab >>Atomistic simulations of lattice defects
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Mechanical properties of solids are governed by crystal imperfections. Computational materials science is largely concerned with the modelling of such defects, e.g. their formation, migration, and interaction energies. Atomistic simulations of systems containing lattice defects are inherently difficult because of the generally complicated geometrical structure of the defects, the need for large simulation cells, etc.

In this thesis, the role of lattice defects in the mechanism behind homogeneous melting is demonstrated. Also, a generic calculational scheme for studying atomic vibrations close to extended defects (applied to a dislocation) has been considered. Furthermore, heat capacities in the solid and liquid phases of aluminium have been calculated, as well as various thermophysical defect properties.

The work was carried out using classical atomistic simulations, mainly molecular dynamics, of aluminium and copper. The interatomic forces were modelled with effective interactions of the embedded-atom type.

The main results of this thesis are the following:

• The thermal fluctuation initiating melting is an aggregate typically with 6-7 interstitials and 3-4 vacancies.

• In the initial stage of melting, no signs of a shear modulus melting mechanism, or the presence of line-like defects (dislocations), can be seen.

• The typical time interval from when melting initiates to the time at which the liquid phase is fully developed is of the order of 1000τ, where the period τ corresponds to the maximum vibrational frequency in the solid.

• The solid-liquid boundary advances at a pace comparable to that of thermal transport by vibrating atoms in the crystal at high temperatures.

• The seemingly small anharmonic effect in the heat capacity of aluminium is caused by a partial cancellation of the low-order term linear in the temperature and anharmonic terms of higher order in the temperature.

• The core region of an edge dislocation in face-centred cubic aluminium has compressed and expanded regions. The excess volume associated with the dislocation core is small, about 6 percent of the atomic volume, as a result of a partial cancellation between the volume changes of the compressed and expanded regions.

• The compressed and expanded regions of the edge dislocation core give negative and positive contributions, respectively, to the excess vibrational entropy. The overall effect is a positive vibrational excess entropy of the dislocation core which is about 2kB per atomic repeat length along the dislocation core.

• The atomic vibrations near the dislocation core are modelled by considering an atomic cluster with about 500-1000 atoms containing the core of dislocation, embedded in a large discrete, but relaxed, lattice of about 23 000 atoms. An atomic region that is four atomic layers thick and about 18 atomic diameters long in the direction parallel to the Burgers vector, accounts for most of the excess entropy.

• The constant-pressure heat capacity of aluminium shows a minimum as a function of temperature in the liquid phase.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. vii, 64 p.
Trita-FYS, ISSN 0280-316X ; 2005:26
Theoretical physics, Teoretisk fysik
National Category
Physical Sciences
urn:nbn:se:kth:diva-253 (URN)91-7178-042-4 (ISBN)
Public defence
2005-06-07, Sal FB42, AlbaNova, Roslagstullsbacken 21, Stockholm, 13:00
QC 20101013Available from: 2005-06-01 Created: 2005-06-01 Last updated: 2010-10-13Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Forsblom, MattiasGrimvall, Göran
By organisation
Theory of Materials
In the same journal
Physical Review B. Condensed Matter and Materials Physics
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 38 hits
ReferencesLink to record
Permanent link

Direct link