Review of the molecular dynamics of molten salt thermal physical properties
FU Dianwei,, ZHANG Cancan,, NA Heya, WANG Guoqiang, WU Yuting, LU Yuanwei
MOE Key Laboratory of Enhanced Heat Transfer and Energy Conservation, BeijingKey Laboratory of Heat Transfer and Energy Conversion, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China
As a high-temperature heat transfer and storage medium, molten salt is widely used for solar thermal power generation and the flexible transformation of thermal power plants. First, the potential functions of the molecular dynamics of molten salt were summarized and analyzed. This indicated that to reduce simulation errors, the Buckingham potential with coulomb force is more suitable for nitrate and the BMH potential is more suitable for carbonate and chloride salt. Second, an analysis of the thermal properties of molten salt indicated that the addition of Ca2+ to solar salt decreased its melting point and increased its viscosity, and the specific heat capacity of nitrate decreased with increasing NO2- concentration. Increased Li+ concentrations increased the specific heat capacity and thermal conductivity of chloride salt but also increased the simulation error; however, with increased K+, the specific heat capacity error decreased and the error when calculating residual heat properties increased. The carbonate simulation error was relatively small, which is consistent with experimental results. The simulation errors were large with the addition of K+ or Li+, and the increased potential energy between ions led to the loss of some particles. It was found that the influence of the boundary effect after the introduction of a boundary condition increased the error; however, the error was reduced by increasing the number of molecules, the potential energy truncation distance correction, and the simulation time step. Currently, studies on the molecular dynamics of molten salt with the same cation and different anions are rare. Exploring the influence of nanofluids on molten salt molecular dynamics, reducing the simulation error of molecular dynamics, and conducting research on the corrosion characteristics of molten salt based on molecular dynamics is the next research direction of molten salt molecular dynamics.
Keywords：molten salt
;
molecular dynamics
;
potential function
;
thermophysical property
FU Dianwei. Review of the molecular dynamics of molten salt thermal physical properties[J]. Energy Storage Science and Technology, 2023, 12(12): 3873-3882
Fig. 2
The flow chart of molten salt molecular dynamics
1.1 势函数的研究进展
分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础。
分子动力学模拟通常选择CVFF (consistent valence force field)力场或者UFF (universal force field)力场。CVFF力场属于传统力场，适用于有机小分子体系，主要预测分子结构和自由能；UFF力场通常适用于所有元素。早期的原子间相互作用势，大多是一些纯经验拟合势，近年来通过对基本电子结构的理论计算，根据对系统总能量的贡献将其分为两类：①总能量由势函数决定，可有效描述范德瓦耳斯互作用占据主导地位的体系；②势函数仅仅描述恒定材料平均密度下系统的能量随原子构型的变化，适用于描述sp-价态金属。本文对熔盐常用的势函数类型、计算公式及对应熔盐进行了总结，如表1所示。
Table 1
表1
表1熔盐分子动力学模拟势函数
Table 1 Molten salt molecular dynamic simulation potential functions
分子动力学计算中用到多种公式，决定分子间的相互作用力。常用的一些公式包括径向分布函数(radial distribution function，RDF)、配位数N(r)、自扩散系数D、均方位移(mean square displacement，MSD)、角分布函数(angular distribution function，ADF)、热导率等，如表2所示。
Fig. 3
The variation of diffusion degree with temperature and coordination number of , ion pairs and Ca2+, ion pairs: (a) , ion pair; (b) Ca2+, ion pair
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... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
1
... 分子动力学模拟结果准确性与系统内原子间相互作用势的选取存在直接关系[17]，1924—1984年，学者先后提出了Lennard-Jones(LJ)[18]、Morse[19]、Born-Mayer[20]、Buckingham[21]、Busing[22]和Embedded Atom Method(EAM)[23]势函数解析式，为熔盐分子动力学研究奠定了基础. ...
2
... Molten salt molecular dynamic simulation potential functionsTable 1
