Kai Kadau's web pages:
home page
molecular-dynamics
simulations movie page
graphic
page
sport page
old MPEG-movie page (this
page)
Molecular-dynamics simulation movies
The MPEG-movies
download able are results of molecular-dynamics simulations. The method
of molecular-dynamics simulation give insight into atomic processes of
a physical system and yields the time evolution on time scales between
femto seconds and nano seconds.
Most of the simulations were performed
by using an embedded-atom method (EAM) potential (M.S. Daw and M.I. Baskes
PRL 50, 1285 (1983.), ) M.S. Daw and M.I. Baskes PRB 29, 1285 (1983.) which
consist of a density depend and a two body potential term. The EAM potential
is able to reproduce fundamental properties of metals in contrast to pure
pair-potentials like the Lenard-Jones (LJ) potential. Different ensembles
are used including the 'natural' NVE, NVT, and the NPT ensemble in different
realizations like the Parinello-Rahman scheme (allowing the change of shape
and size of the simulation box) and the Anderson scheme (isotropic volume
fluctuations).
These movies are results of earlier
simulations where the number of atoms is very limited, for more recent
movies go to the SPaSM
large scale molecular-dynamics home page or to Kai's SPaSM-movie
page.
Nanophase materials (nanocrystalline
materials):
We model the consolidation process
of a nanophase Iron-Nickel alloy from atom clusters at room temperature.
The isolated clusters, each containing about 1000 atoms, initialized in
the bcc structure transform into the fcc structure before contacting each
other. After some simulation time they begin to contact by forming necks.
During the consolidation process the voids are getting smaller. Clearly
visible is the slipping of different fcc(111)-planes. At the the end of
the simulations the consolidation of the nanophase material is about 96
percent of the bulk value for the simulated alloy. The vertical pressure
increases from zero to aprox 8 GPa. The total real-time showed in the movie
is 60 pico seconds, one picture is the average of 750 femto seconds.
Movie13
(consolidation process)(9MB)
Fe on Cu(001):
At 300K a 15 ML Fe slab on a Cu(001)-substrate
is cooled down. In this movie you can follow the increasing bcc-formation
with decreasing temperature. In the first picture the whole sample is shown
(Fe atoms blue and Cu atoms orange). In the following movie the Fe-film
is shown slice-wice whereas the bcc structure is shown in blue and the
fcc structure in orange. The sample contains approximately 40000 atoms.
The whole playing time is 12 pico seconds.
Movie Fe on
Cu (2.5 MB)
The second movie shows an Fe-Island
on a Cu(001)-substrate. Here the main nucleation process starts at the
border of the island. In contrast to the complete Fe-film the amount of
transformed Fe is significantly higher, due to the lack of lateral stress.
Movie
Fe-Island on Cu (2.0 MB)
Martensitic transformations
(here actually austenitic transformations)
of an unordered Iron (80 percent) Nickel (20 percent) alloy due to heating(425K-1225K)
are shown. The sample (consists of 686 atoms) change from a bcc structure
into a twinned and other stacking faults including fcc structure at a temperature
of approximately 900K (due to high heating rates the sample is overheated).
The iron atoms are the blue and the nickel atoms are the orange spheres.
The total real time showed in the movies is 15 pico seconds, one picture
is the average of 30 femto seconds:
Movie1(whole
sample is shown)(7MB)
Movie2(part
of the sample is shown)(6MB)
Movie3(bcc
cubic unit cell is shown)(4MB)
Movie4(bcc(110)-plane
transforming into fcc(111) is shown)(6MB)
Movie5(Something
else is shown(one picture is the average of 75 femto seconds))(8MB)
The next two movies (similar sample
like above) show the nucleation of austenite (here fcc) during heating
(425K-1225K) and the nucleation of martensite (here bcc) during cooling
(1175K-10K). The time scale for this movies are larger because here the
germination dynamics is of interest and not the atom dynamics. One picture
is the average of 600 femto seconds, the total time showed in these movies
is 240 pico seconds. Here the blue color indicates the martensite (bcc)
and the orange color the austenite (fcc). After the back transition the
sample regains the original shape which is a kind of shape memory effect,
which is of technological interest. In the simulations the shape memory
effect occurs because of the reduced symmetry of the transformed sample
due to the micro structure (twinning, stacking faults).
Movie6(heating)(3MB)
Movie7(cooling)(3MB)
Friction scenario:
At 300K a Nickel tip (pyramidal
trunk) in the fcc-structure slides over an iron substrate which is in the
bcc-structure. The sample contains approximately 9000 atoms. Both contacting
surfaces are the (100) surfaces. In this geometry the contact is performed
by simple elongation. In the movie the pictures are averages of 12 pico
seconds, so that the whole playing time is about 300 pico seconds. This
simulations are attempts to describe an atomic-force microscope (AFM) with
means of molecular-dynamics Simulations. Nickel atoms remaining on the
bcc surface arrange according to the substrate structure in the bcc structure.
Movie9
(slow tip velocity (10m/s))(0.5MB)
Contact scenario:
At 50K a Nickel tip (pyramidal trunk)
and a nickel substrate were brought together with a remaining chink of
half a lattice constant. The sample consist of approximately. 4000 atoms.
Both surfaces are (111)-surfaces. The contact is due to the forming of
an additional layer. The mechanism of forming the additional layer seems
to be connected with a ductile crack process. In the case of (100) surfaces
the contact is due to simple elongation. The total real time showed in
the movies here is 2.25 pico seconds (one picture is the average over 75
femto seconds). This simulations are also attempts to describe an atomic-force
microscope (AFM) with means of molecular-dynamics simulations:
Movie10 (view
in the [-110]-direction)(0.5MB)
Movie11
(view in the [11-2]-direction (0.5MB)
Homes
Theoretical
Low-Temperature Physics (University Duisburg, Germany)
Theoretical
Division (T-11) (LANL, USA)
Kai Kadau's
home page