A molecular dynamics study of the effect of Coulomb Buckingham Potential on equilibrium structural properties of calcium titanate perovskite

Ibrahim Almishal Saeed Sameer,Hatem Tarek M.,El-Mahallawi Iman S. 한국물리학회 2022 Current Applied Physics Vol.40 No.-

The demand on new and highly efficient energy conversion systems and many other advanced applications have suggested perovskites to be important future candidate materials. Though a lot of work has been done to understand and model their structure and properties, further investigation is still needed. Consequently, the development and enhancement of computational methods including molecular dynamics and quantum chemical calculations is one of the main issues regarding the understanding and optimization of perovskites. In this work, Coulomb Buckingham interatomic potential function is investigated to analyze the structure of Calcium Titanate CaTiO3 through the application of Molecular Dynamics via LAMMPS open source code. The results are compared with the results of other potential functions representations, namely Vashishta-Rahman (VR) and Lennard-Jones (LJ) potentials. The understanding of the effect of potential representation on structural properties would lead to deduction of mechanical and thermal properties and to building a platform for adapting the different types of oxide perovskites, or even nonorganic halide perovskites, to enhance their technological aspects. The VR interaction potential was previously proven to be the most effective for describing the phase changes of perovskites and to match the experimental observations. It was also proven in previous studies that the radial distribution function (RDF) undergoes essential changes when replacing LJ with VR. According to the findings of this study, Buckingham potential is shown to produce much closer results to VR than LJ of the radial distribution function.

소산입자동역학과 분자동역학을 이용한 3D 프린터용 PEEK 분말에 대한 온도에 따른 미시적 구조변화에 대한 연구

김남원(Namwon Kim),이태일(Taeil Yi) 한국기계가공학회 2018 한국기계가공학회지 Vol.17 No.5

3D printing technology and its applications have grown rapidly in academia and industry. We consider a 3D printing system designed for the selective laser sintering (SLS) method, which is one of the powder bed fusion (PBF) techniques to build up the final product by layering sintered powder slices. Thermal distortion of printing products is a critical challenge in 3D printing. This study investigates temperature-dependent conformational behaviors of 3D printed samples of sintered poly-ether-ether-ketone (PEEK) powders using molecular dynamics simulations. The wear and chemical resistance properties of PEEK are understood, as it is a well-known biocompatible material used for implants. However, studies on physical phenomena at nanoscale in PEEK are rarely published in public. We simulate dissipative particle dynamics to elucidate how a cavity regime forms in PEEK at different system temperatures. We demonstrate how PEEK structures deform subject to the system temperature distribution.

Effects of gradient on stress distribution in rotating functionally graded solid disks

Xu-Long Peng,Xian-Fang Li 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.5

"This paper presents the elastic analysis of a rotating sandwich solid disk composed of three-layered perfectly-bonded composites. The center and outer regions of the solid disk are two homogeneous isotropic media, and the middle region is a transition zone made of functionally graded materials (FGM). Two cases are considered. One is on FGM with power-law gradient. For this case, explicit expressions for full elastic fields are derived. The other is on FGM with any radial nonhomogeneity, for which an analytic approach is proposed to reduce the problem into a Fredholm integral equation. The validity of the latter method is ensured by comparing numerical results of the elastic fields with the exact ones for the case of power-law gradient. For a general case, the current study presents the influences of the gradient, width variation of the FGM, and rotational velocity on the distribution of the radial and hoop stresses for a rotating composite disk made of aluminum and zirconia. The method presented in this paper may help engineering designers in choosing appropriate gradients and materials to acquire the optimal state of a rotating functionally graded disk."

YHB 동경분포함수에 의한 기체 분자의 압력 계산

윤종호 ( Jong Ho Yoon ),박명수 ( Myung Soo Park ),이택홍 ( Taeck Hong Lee ) 한국공업화학회 2002 공업화학 Vol.13 No.8

-50∼100 ℃의 온도 범위에서 밀도 변화에 따른 CH_4, CO, 그리고 CO_2 기체의 압력을 YHB 동경분포함수를 이용하여 계산하였다. 이 계산의 목적은 주로 온도 범위 100∼300 ℃, 압력 범위 300∼3000 atm의 고온 고압의 조건의 기체 시스템의 거동을 조사할 때 사용하던 YHB 동경분포함수를 저온 범위로 확장하여 저온 기체시스템에서의 YHB 동경분포함수의 적용성 여부를 연구하였다. YHB 동경분포함수의 구성에 사용된 포텐샬은 CO와 CO_2기체 분자의 분자간 쌍극자와 사중 극자 상호작용을 포함시키기 위한 Stockmayer 포텐샬이다. 압력의 계산은 1∼1000 atm의 범위에서 실시하였다. 계산한 기체의 압력은 조사된 모든 온도에서 약 10% 내의 오차범위 내로 문헌에 나타난 실험치와 잘 일치하였다. 이는 YHB 동경분포함수가 각종 기체들의 저온에서의 거동을 신뢰성 있게 다룰 수 있다는 것을 나타낸다. Density-dependent pressures of gaseous CH_4, CO, and CO_2 were calculated by using the YHB radial distribution function at the temperatures -50∼100 ℃. The purpose of this study is to examine the applicability of YHB radial distribution function for low temperature behaviors of gas molecules which has been used mainly to examine high temperature and high pressure behavior of gaseous molecules at the temperature range of 100∼300 ℃ and the pressure range of 300∼3000 atm. The intermolecular potential function used was Stockmyer potential. This is to include intermolecular dipolar and quadrupolar interactions of CO and CO_2 molecules properly. The presures calculated were 1∼1000 atm. The calculated pressures corresponded well with literally known experimental data within 10% of error range. This indicated that the YHB radial distribution function is good enough to handle low temperature behavior of gas molecules.

The Radial Distribution Functions of the Scaled OSS2 Water

Lee, Song Hi Korean Chemical Society 2012 대한화학회지 Vol.56 No.6

Classical molecular dynamics (MD) simulations using a scaled OSS2 potential originally derived from ab initio calculations are used to study the radial distribution functions of water. The original OSS2 water potential is shown to represent a glassy or an ice at ambient temperature, but the diffusion coefficient increases on increasing the temperature of the system or decreasing the density. This suggests scaling the OSS2 potential. The O-O, O-H, and H-H radial distribution functions and the corresponding coordination numbers for the scaled OSS2 potential, obtained by MD simulation, are in good agreement with the experiment results and calculations for the SPC/E water potential over a range of temperatures.

Anisotropic Phase Transitions of Hard-Spheres Confined in Hard Walls

윤병집,Yun, Byeong Jip Korean Chemical Society 2001 Bulletin of the Korean Chemical Society Vol.22 No.12

Monte Carlo simulations of hard-spheres confined in parallel hard walls have been carried out extensively at various densities and for various wall distances. The compressibility factors in the directions parallel and normal to the wall have been calculated from the radial free space distribution function (RFSDF) with the results showing that the compressibility factors normal to the wall are smaller than those in parallel direction and that a solid phase is formed in the direction normal to the wall while a fluid phase remains in the parallel direction. An order parameter is found to classify the phases whether a system (or a molecule) is in a fluid or a solid state. The compressibility factors of narrow wall are very small compared to those when the wall is put away. A plausible mechanism of the rise of sap in xylem vessel has been proposed.

Microstructure and shear modulus in concentrated dispersions of bidisperse charged spherical colloids

전명석,이상우,이태석,Jae Seol Cho 한국유변학회 2004 Korea-Australia rheology journal Vol.16 No.1

We examine rigorous computations on microstructural as well as rheological properties of concentrated dispersions of bidisperse colloids. The NVT Monte Carlo simulation is applied to obtain the radial distribution function for the concentrated system. The long-range electrostatic interactions between dissimilar spherical colloids are determined using the singularity method, which provides explicit solutions to the linearized electrostatic field. The increasing trend of osmotic pressure with increasing total particle concentration is reduced as the concentration ratio between large and small particles is increased. From the estimation of total structure factor, we observe the strong correlations developed between dissimilar spheres. As the particle concentration increases at a given ionic strength, the magnitude of the first peak in structure factors increases and also moves to higher wave number values. The increase of electrostatic interaction between same charged particles caused by the Debye screening effect provides an increase in both the osmotic pressure and the shear modulus. The higher volume fraction ratio providing larger interparticle spacing yields decreasing high frequency limit of the shear modulus, due to decreasing the particle interaction energy.

Microstructure and shear modulus in concentrated dispersions of bidisperse charged spherical colloids

Chun, Myung-Suk,Lee, Sangwoo,Lee, Tae-Seok,Cho, Jae-Seol The Korean Society of Rheology 2004 Korea-Australia rheology journal Vol.16 No.1

We examine rigorous computations on microstructural as well as rheological properties of concentrated dispersions of bidisperse colloids. The NVT Monte Carlo simulation is applied to obtain the radial distribution function for the concentrated system. The long-range electrostatic interactions between dissimilar spherical colloids are determined using the singularity method, which provides explicit solutions to the linearized electrostatic field. The increasing trend of osmotic pressure with increasing total particle concentration is reduced as the concentration ratio between large and small particles is increased. From the estimation of total structure factor, we observe the strong correlations developed between dissimilar spheres. As the particle concentration increases at a given ionic strength, the magnitude of the first peak in structure factors increases and also moves to higher wave number values. The increase of electrostatic interaction between same charged particles caused by the Debye screening effect provides an increase in both the osmotic pressure and the shear modulus. The higher volume fraction ratio providing larger interparticle spacing yields decreasing high frequency limit of the shear modulus, due to decreasing the particle interaction energy.

분자동역학을 이용한 열원 주변에서의 나노입자의 분포에 대한 연구

이태일(Taeil Yi) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.5

Since nanofluids (NFs), which are a mixture of a small amount of nanoparticles and a bulk liquid solvent, were first proposed by Stephen Choi at the Argonne National Lab in 1995, they have been considered for use in many technical studies of power cooling systems and their practical application due to their high thermal conductivity and heat transfer coefficients compared to conventional coolants. Although nanofluids are a well-known form of engineering fluid that show great promise for use in future cooling systems, their underlying physics as demonstrated in experiments remain unclear. One proven method of determining the heat transfer performance of nanofluids is measuring the concentration of nanoparticles in a mixture. However, it is experimentally inefficient to build testbeds to systematically observe particle distributions on a nanoscale. In this paper, we demonstrate the distribution of nanoparticles under a temperature gradient in a solution using molecular dynamics simulations. First, temperature profiles based on substrate temperature are introduced. Following this, the radial pair distribution functions of pairs of nanoparticles, solvents, and substrates are calculated. Finally, the distribution of nanoparticles in different heating regions is determined.

Structural Arrangement of Water Molecules around Highly Charged Nanoparticles: Molecular Dynamics Simulation

김은애,염민선 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.5

Molecular dynamics simulations were performed to understand the structural arrangement of water molecules around highly charged nanoparticles under aqueous conditions. The effect of two highly charged nanoparticles on the solvation charge asymmetry has been examined. We calculated the radial distribution functions of the components of water molecules around nanoparticles which have four charge types at two different salt concentrations. Even though the distributions of water molecules surrounding a sodium ion and a chloride ion are hardly affected by the charges of nanoparticles and the salt concentrations, those around highly charged nanoparticles are strongly influenced by the charges of nanoparticles, but hardly by the charges of nanoparticles and salt concentrations. We find that the distributions of hydrogen atoms in water molecules around one highly charged nanoparticle are dependent on the magnitude of the nanoparticle charge.