Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Melting evolution of Fe nanoparticles from molecular dynamics simulations
Serap Senturk Dalgic ,1 *, Cem Canan 1 and Oguz Gulseren 2
1 Department of Physics, Trakya University, Edirne, 22030, Turkey
2 Department of Physics. Bilkent University. Bilkent, Ankara 06800, Turkey
Abstract–In order to study the melting properties of bcc metal iron nanoparticles, molecular dynamics calculations have been performed for
various nanoparticles with different number of atoms. The modified analytic embedded atom method (MAEAM) interatomic potentials are
used to describe the interaction between Fe atoms. The melting process can be described as occurring in two stages, firstly the stepwise
premelting of the surface layer with a thickness of 2–3 times the perfect lattice constant, and then the abrupt overall melting of the whole
nanoparticle. The melting point and heat of fusion of nanoparticles are inversely proportional to the reciprocal of the nanoparticle size. We
have also studied the structural evolution of Fe nanoparticles with different temperature. Radial distribution functions are adopted to explore
structural transition. In addition, dynamic properties of Fe nanop articles such as diffusion coefficient (D), mean square displacement (MSD)
have been calculated.
There are various reasons for the great interest in iron
(Fe) nanoparticles. Generally, magnetic nanoparticles are
receiving a lot of attention today because of several
possible applications. Hence, owing to its magnetic
properties, there is special interest in iron. Indeed, iron
nanoparticles have attracted special attention because they
may be used in power-transformer cores and magnetic
storage media as well as for catalysis (see the good review
about the synthesis, properties and applications of Fe
nanoparticles of Huber [1]). Iron nanoparticles can be
produced in both forms, i.e. in crystalline and amorphous
phases, and much attention has been paid to the latter in
recent years [2]. We found only a few works related to the
computer simulation of crystalline Fe nanoparticles [3–5].
In the present study, the melting process of Fe
nanoparticles with the number of atoms ranging from 2741
to 44375 (diameters around 4–10 nm) has been simulated
by using modified analytic embedded atom method
(MAEAM) [6]. During melting process, we have studied
mean atomic energy changes with respect to the
temperature for bulk Fe and four Fe nanoparticles. Then,
we have also interested in how the melting temperature and
heats of fusion depend on size of nanoparticles. The static
and dynamic structural properties have been calculated for
four nanoparticles with different sizes and then structural
transitions have been investigated in detail. The initial
configurations of spherical nanoparticles, with
nanoparticles diameter 4, 6, 8, 10 nm, are extracted from a
large BCC crystal structure of spherical cutoff centered at a
core of cubes. All of the atoms are located on their lattice
positions. The stable structure at 0 °K is obtained through
the initial configurations annealed fully at T=300 °K and
then cooled to T=0 °K at a cooling rate 0.5 K/ps. In order to
get an energy-optimized structure during heating at a given
temperature for bulk systems, molecular dynamics
calculations under constant temperature and constant
pressure conditions (NPT) with periodic boundary
conditions have been performed. For the nanoparticles, we
used the constant volume and constant temperature (NVT)
molecular dynamics without the periodic boundary
conditions. The temperature is controlled by Nose-Hoover
thermostat. Newtonian equations of motion are integrated
using the Leapfrog Verlet method with a time step 2 fs. For
bulk and nanoparticles, system is subjected to heating
process consisting of a series of MD simulations with
temperature increments T=50 °K and relaxing time 100ps.
However, for a temperature near the melting region, we
have used smaller temperature increment, T=10 °K, wh ile
keeping the relaxation time as 100 ps.
For the investigation of melting evolution and
distinctive surface properties, two spherical shell regions
with the same thickness of a 0 are divided and labeled as A,
B, starting fromthe outmost shell, and the remaining core is
labeled as C analyzed respectively as shown in Figure 1.
T =300 °K T =900 °K T =1200 °K T =1800 °K
Figure 1. x-y coordinate snapshot views of the MD sample with
N=9577 (D=6nm) at a series of temperatures during heating with
layers A, B, C(core) yellow, brown and red respectively.
To conclude, we have investigated the melting evolution
of iron nanoparticles from molecular dynamics simulations
using a modified analytic embedded-atom potential. The
evolution of atomic configuration and energy with
temperature reveals that the melting process of iron
nanoparticles can be described in two stages, the stepwise
premelting from the outmost surface and the sudden
melting in the inner core. The thickness of the liquid skin
resulting from the surface premelting is discrepant for
particles with different diameters. Owing to the two stages
melting, the heat of melting for nanoparticles should
involve two parts. As the particle size decreases, the heat of
melt decreases correspondingly. The atomic diffusion in
nanoparticles is mainly localized to the surface layers
before the melting temperature and increases with the
reduction of particle size at the same temperature.
* Corresponding author: dserap@yahoo.com
[1] Huber D L Small 1, 482 (2005)
[2] Hoang V. V, Nanotechnology, 20, 295703 (2009).
[3] Postnikov A V, Entel P and Soler J M, Eur. Phys. J. D 25
261 (2003)
[4] Rollmann G, GrunerM E, Hucht A, Meyer R, Entel P,
Tiago M L and Chelikowsky J R, Phys. Rev. Lett. 99 083402
(2007)
[5] Shibuta Y and Suzuki T, Chem. Phys. Lett. 445 265 (2008)
[6] 0TZhang J, Wen Y, Xu K, Central European Journal of
Physics, 4, 481 (2006)
6th Nanoscience and Nanotechnology Conference, zmir, 2010 342