Phase separation of Si1-xGex alloys

1995 ◽  
Vol 378 ◽  
Author(s):  
Eunja Kim ◽  
Young Hee Lee
Keyword(s):  
Molecular Dynamics ◽  
Distribution Function ◽  
Phase Separation ◽  
Bond Angle ◽  
Alloy System ◽  
Order Parameters ◽  
Angle Distribution ◽  
Bond Angle Distribution ◽  
Random Alloy ◽  
Amorphous Si

AbstractWe generate liquid and amorphous Si1_xGex alloys for various Ge compositions using ab initio molecular dynamics approach. The electronic bonding characters and structural properties are discussed in terms of radial distribution function, bond angle distribution, and order parameters. Although the order parameters suggest approximately random alloy for all compositions, the snapshots reveal clearly phase separation. We will discuss how the phase can be separated in SiGe alloy system.

THE CORRELATION BETWEEN BOND ANGLE DISTRIBUTION AND THE COORDINATION OF SILICA LIQUID UNDER PRESSURE

2012 ◽  
Vol 26 (20) ◽  
pp. 1250117 ◽  
Author(s):  
L. T. VINH ◽  
N. V. HUY ◽  
P. K. HUNG
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Bond Angle ◽  
Simple Expression ◽  
Dynamics Simulation ◽  
Angle Distribution ◽  
Bond Angle Distribution ◽  
Simulation Results ◽  
Substantial Change ◽  
Good Agreement

Molecular dynamics simulation is carried out for liquid SiO 2 at pressure ranged from zero to 30 GPa and by using BKS, Born–Mayer type and Morse–Stretch potentials. The constructed models reproduce well the experimental data in terms of mean coordination number, bond angle and pair radial distribution function. Furthermore, the density of all samples can be expressed by a linear function of fractions SiO x. It is found that the topology of units SiO x and linkages OSi y is unchanged upon compression although the liquid undergoes substantial change in its network structure. Consequently, the partial bond angle distribution for SiO x and OSi y is identical for all samples constructed by the same potential. This result allows to establishing a simple expression between total bond angle distribution (BAD) and fraction of SiO x and OSi y. The simulation shows a good agreement between the calculation and simulation results for both total O–Si–O and Si–O–Si BADs. This supports a technique to estimate amount of units SiO x and linkages OSi y on base of total Si–O–Si and O–Si–O BADs measured experimentally.

Structure and Properties of the GeAsS Glasses from Ab initio Calculations

2014 ◽  
Vol 1035 ◽  
pp. 502-507
Author(s):  
Li An Chen
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Ab Initio ◽  
Bond Angle ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Angle Distribution ◽  
Structure And Properties ◽  
Bond Angle Distribution ◽  
Pair Distribution Functions

The structure and properties of the GexAsxS100-2x have been studied by ab initio molecular dynamics simulation. By calculating the pair distribution functions, bond angle distribution functions, we analyze the structure and properties of the alloys. Calculations show that Ge and As are all well combined with S atoms. When x is smaller than 25.0 the binding increases with x , when x is larger than 25.0 the binding decreases with increasing x . The intervention of As atom does not affect the GeS2 formation in Ge40As40S80

MICROSTRUCTURAL EVOLUTION OF SiC DURING MELTING PROCESS

2013 ◽  
Vol 27 (31) ◽  
pp. 1350231 ◽  
Author(s):  
WANJUN YAN ◽  
QUAN XIE ◽  
TINGHONG GAO ◽  
XIAOTIAN GUO
Keyword(s):  
Distribution Function ◽  
Microstructural Evolution ◽  
Bond Angle ◽  
Melting Process ◽  
Angle Distribution ◽  
Microstructural Characteristics ◽  
Voronoi Polyhedron ◽  
Bond Angle Distribution ◽  
Tetrahedral Bond ◽  
Simulation Results

Microstructural evolution of SiC during melting process is simulated with Tersoff potential by using molecular dynamics. Microstructural characteristics are analyzed by radial distribution function, angle distribution function and Voronoi polyhedron index. The results show that the melting point of SiC with Tersoff potential is 3249 K. Tersoff potential can exactly describe the changes of bond length, bond angle and Voronoi clusters during the process of melting. Before melting, the length of the C – C bond, Si – Si bond and Si – C bond is 3.2, 3.2 and 1.9 Å, respectively. The bond angle distributes near the tetrahedral bond angle 109°, and the Voronoi clusters are all (4 0 0 0) tetrahedron structures. After melting, the C – C bond and Si – Si bond are reduced, while the Si – C bond is almost unchanged. The range of bond angle distribution is wider than before, and most of the (4 0 0 0) structures turn into three-fold coordinated structures, (2 3 0 0), (0 6 0 0) and (2 2 2 0) structures. The simulation results clearly present the microstructural evolution properties of SiC during the melting process.

The Effect of Pressure on the Hydrogen Bond Structure of Liquid Water

1984 ◽  
Vol 39 (2) ◽  
pp. 179-185 ◽  
Author(s):  
G. Pálinkás ◽  
P. Bopp ◽  
G. Jancsó ◽  
K. Heinzinger
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Liquid Water ◽  
Bond Angle ◽  
Angle Distribution ◽  
Structure Of Water ◽  
Effect Of Pressure ◽  
Bond Angle Distribution ◽  
Dynamics Simulations ◽  
Force Potential

The results of molecular dynamics simulations of low and high pressure liquid water using a modified central force potential have been analyzed in order to study the effect of pressure on the hydrogen bond structure of water. The properties investigated and discussed include the hydrogen bond angle distribution, the O -O distance distribution between the neighbour molecules, the structure of the first coordination sphere in the high density liquid and the average number of hydrogen bonds.

AB INITIO MOLECULAR DYNAMICS SIMULATIONS ON LOCAL STRUCTURE AND ELECTRONIC PROPERTIES IN LIQUID MgxBi1-x ALLOYS

2013 ◽  
Vol 27 (06) ◽  
pp. 1350011 ◽  
Author(s):  
QING-HAI HAO ◽  
YU-WEI YOU ◽  
XIANG-SHAN KONG ◽  
C. S. LIU
Keyword(s):  
Molecular Dynamics ◽  
Local Structure ◽  
Order Parameter ◽  
Bond Order ◽  
Bond Angle ◽  
Pair Correlation ◽  
Ab Initio Molecular Dynamics ◽  
Angle Distribution ◽  
Bond Angle Distribution ◽  
Dynamics Simulations

The microscopic structure and dynamics of liquid Mg x Bi 1-x(x = 0.5, 0.6, 0.7) alloys together with pure liquid Mg and Bi metals were investigated by means of ab initio molecular dynamics simulations. We present results of structure properties including pair correlation function, structural factor, bond-angle distribution function and bond order parameter, and their composition dependence. The dynamical and electronic properties have also been studied. The structure factor and pair correlation function are in agreement with the available experimental data. The calculated bond-angle distribution function and bond order parameter suggest that the stoichiometric composition Mg 3 Bi 2 exhibits a different local structure order compared with other concentrations, which help us understand the appearance of the minimum electronic conductivity at this composition observed in previous experiments.

Molecular Dynamics Simulation of Size Effect on the Mechanical Properties of Amorphous Silica

2015 ◽  
Vol 30 ◽  
pp. 59-67
Author(s):  
Fang Li Duan ◽  
Cheng Zhang ◽  
Qing Song Liu
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Size Effect ◽  
Amorphous Silica ◽  
Bond Angle ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Angle Distribution ◽  
Small Model ◽  
Large Model

The frustules of diatoms have excellent elasticity and high strength, but their main composition, amorphous silica, is a kind of typical brittle material. Molecular dynamics simulations of the uniaxial tension were carried out to study the size effect on the mechanical properties of amorphous silica. Stress-strain behavior, the radius of biggest void, radial distribution functions and bond angle distribution were analyzed. Our results show the small model exhibits a better ultimate strength, ductility and toughness than the large model, and the generation and expansion of voids plays an important role in the fracture behavior of the model. For the small model, some of Si-O bonds are stretched, and the average of O-Si-O bond angle decreases from 108o to 95o, which makes the model have a capability to perform larger plastic deformation and lead to a better ductility. However, for the large model, except the change of Si-O-Si bond angle, its structure has no other significant changes. Our results demonstrate that changes of size have significant impact on the mechanical properties and deformation mechanism of intrinsically brittle materials at the nanoscale.

scholarly journals Structure and Correlation Between the Fraction of Structural Units and Bond Angle Distribution in Liquid B2 O3 Under Compression

2018 ◽  
Vol 2 (1) ◽  
Keyword(s):  
Pressure Range ◽  
Bond Angle ◽  
Structural Heterogeneity ◽  
Dynamics Simulation ◽  
Angle Distribution ◽  
Structural Units ◽  
Dynamical Heterogeneity ◽  
Heterogeneous Dynamics ◽  
Bond Angle Distribution ◽  
Spatially Heterogeneous Dynamics

Structure of network-forming liquid B2 O3 is investigated by Molecular dynamics simulation (MDS) at 2000K and in the 0-40 GPa pressure range (corresponding to the 1.71-3.04 g/cm3 density range). Results indicate that network structure of liquid B2 O3 comprises of basic structural units BO3 and BO4 . The topology and size of BO3 and BO4 units at different densities are identical. The O-B-O and B-O-B partial bond angle distributions (BADs) can be determined through the fraction of BO3 and BO4 units. Furthermore, the total BADs are directly related to the partial BADs and the fraction of structural units. It means the fraction of units BOX (X = 3,4) and units OBy (y = 2,3) can be determined from the experimental BADs. The spatial distribution of BO3 and BO4 units is not uniform but forming clusters of BO3 and BO4 . This leads to the polyamorphism in liquid B2 O3 . It also shows that the dynamical heterogeneity in liquid B2 O3 due to the lifetimes of BO3 and BO4 units are very different. The structural heterogeneity is origin of spatially heterogeneous dynamics in liquids B2 O3 .

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