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1.
本文采用微正则分子动力学方法模拟研究了铂、铜和银原子纳米团族从固态到液态的熔化过程,得到热容量随温度变化关系,结果表明这三种金属纳米团簇在熔化过程中均出现了负热容现象,并通过对团簇热能随温度的变化关系以及团簇原子数径向分布的分析,探讨了产生负热容现象的微观机制.  相似文献   

2.
本文采用分子动力学模拟方法,研究了银、钴和铂原子纳米团簇的熔化过程,模型采用的是Johson的EAM作用势.模拟结果表明,较大原子数目的纳米团簇其熔点随尺寸单调增加,而较小原子数目的团簇熔点和尺寸呈现无规则变化;大多数团簇在熔点附近都出现了负热容现象,说明负热容是纳米团簇在熔化过程中的一个普遍现象.  相似文献   

3.
采用分子动力学方法和原子嵌入势模拟了大尺寸金(n=1136~1556)、银(n=1088~1724)、铜(n=1000~1600)、铂(n=1004~1800)原子纳米团簇的熔化过程,得出了相应纳米团簇的势能随温度的变化曲线以及热容量随温度的变化曲线,研究了各种原子纳米团簇熔点与其团簇尺寸的关系.模拟结果表明团簇的熔点随团簇尺寸增大而升高,并逐渐向大块晶体靠拢.所有纳米团簇在熔化过程中在熔点附近都出现负热容现象,通过对团簇熔化前后结构的比较,分析了导致这种现象的原因.  相似文献   

4.
铜原子纳米团簇热力学性质的分子动力学模拟研究   总被引:2,自引:0,他引:2  
利用分子动力学模拟方法,研究了CuN(N=80,140,216,312,408,500,628和736)纳米团簇在热化和冷凝过程中结构和热力学性质的变化,模型采用的是Johnson的EAM作用势.模拟结果表明:铜团簇的熔点和凝固点随其尺寸线性增加,并逐渐向大块晶体靠拢;所有团簇的凝固点都低于熔点,出现凝固过程中的滞后现象;在熔点和凝固点附近,团簇都具有负热容特性,负热容是由相变前后团簇内部结构突变引起的.  相似文献   

5.
本采用分子动力学模拟方法,研究了银、钴和铂原子纳米团簇的熔化过程,模型采用的是Johson的EAM作用势。模拟结果表明,较大原子数目的纳米团簇其熔点随尺寸单调增加,而较小原子数目的团簇熔点和尺寸呈现无规则变化;大多数团簇在熔点附近都出现了负热容现象,说明负热容是纳米团簇在熔化过程中的一个普遍现象。  相似文献   

6.
卢敏  陈巧 《物理实验》2007,27(12):11-14
采用分子动力学方法和嵌入原子法(EAM)多体势函数,模拟研究了银纳米团簇在不同温度直到熔化过程中的结构变化,得到了体系能量和热容量随温度的变化关系.结果显示:银纳米团簇在临近熔点附近出现了负热容现象.研究了弛豫后银纳米团簇的稳态结构变化及其在不同时刻结构的演变过程.结果表明:产生负热容现象的主要原因是纳米团簇在熔点附近,结构发生了巨大的变化,形成由{111}和{100}面围成的结构十分稳定和能量更低的多面体.  相似文献   

7.
本文利用分子动力学模拟方法,研究了CuN(N=80、140、216、312、408、500、628和736)纳米团簇在热化和冷凝过程中结构和热力学性质的变化,模型采用的是Johnson的EAM作用势.模拟结果表明:铜团簇的熔点和凝固点随其尺寸线性增加,并逐渐向大块晶体靠拢;所有团簇的凝固点都低于熔点,出现凝固过程中的滞后现象;在熔点和凝固点附近,团簇都具有负热容特性,负热容是由相变前后团簇内部结构突变引起的.  相似文献   

8.
采用分子动力学方法和原子嵌入模型势模拟了大尺寸金(n=1136--1556)、银(n=1088--1724)、铜(n=1000--1600)、铂(n=1004--1800)原子纳米团簇的熔化过程,得出了相应纳米团簇的势能随温度的变化曲线以及热容量随温度的变化曲线,研究了各种原子纳米团簇熔点与其团簇尺寸的关系。模拟结果表明团簇的熔点随团簇尺寸增大而升高,并逐渐向大块晶体靠拢。所有纳米团簇在熔化过程中在熔点附近都出现负热容现象,通过对团簇熔化前后结构的比较研,分析了导致这种现象的原因。  相似文献   

9.
本文利用分子动力学模拟方法,研究了CuN(N=80、140、216、312、408、500、628和736)纳米团簇在热化和冷凝过程中结构和热力学性质的变化,模型采用的是Johnson的EAM作用势.模拟结果表明:铜团簇的熔点和凝固。点随其尺寸线性增加,并逐渐向大块晶体靠拢;所有团簇的凝固。羔都低于熔点,出现凝固过程中的滞后现象;在熔点和凝固点附近,团簇都具有负热容特性,负热容是由相变前后团簇内部结构突变引起的。  相似文献   

10.
冯黛丽  冯妍卉  张欣欣 《物理学报》2013,62(8):83602-083602
采用分子动力学方法模拟了半径从0.3–1.3 nm变化的小尺寸铝纳米团簇的熔化、凝固行为. 基于势能-温度曲线、热容-温度曲线分析, 获得了熔点、凝固点与尺寸的依变关系, 并利用表面能理论、小尺寸效应开展了现象分析.研究表明, 铝团簇原子数小于80时, 熔点和凝固点的尺寸依赖性出现无规律的异常变化; 而大于该原子数, 熔、凝固点则随着团簇尺寸的减小而单调下降; 当原子数为27时, 团簇熔点高于块材熔点近40 K. 同时, 铝纳米团簇呈现出凝固滞后现象, 即凝固点低于熔点. 关键词: 纳米团簇 熔点 凝固点 分子动力学  相似文献   

11.
Heat capacities have been determined for unsupported aluminum clusters, Al49(+) - Al63(+), from 150 to 1050 K. Peaks in the heat capacities due to melting occur between 450 and 650 K (well below the bulk melting point of 933 K). The peaks for Al+51 and Al+52 are bimodal, suggesting the presence of a premelting transition where the surface of the clusters melts around 100 K before the core. For clusters with n > 55 the melting temperatures suddenly drop, and there is a dip in the heat capacities due to a transition between two solid forms before the clusters melt.  相似文献   

12.
The solid-liquid phase transitions of Lennard-Jones clusters LJN (N=39–55) were simulated by a microcanonical molecular dynamics method using Lennard-Jones potential, and their thermodynamic quantities were calculated. The caloric curves of clusters (except N=42) have S-bend. To understand this behaviour, configurational and total entropies were evaluated, and dents on the entropy curves were taken as a sign of negative heat capacity. The heat capacities were evaluated for N=39–55 clusters using configurational entropy data. The potential energy distributions have bimodal behaviour for all clusters in the given range at the melting temperature. The distinct melting behaviour of LJ42 was explained by the topology of the potential energy surface by examining the isomer distributions at phase transitions for LJ39-LJ55. The isomer distributions were found to be a useful way to interpret this behaviour and melting dynamics in general. Melting temperature, latent heat and entropy change upon melting values were reported and are consistent with literature values and values calculated from bulk thermodynamic properties. The dependence of these quantities on the size of the clusters was examined and it is found that latent heat is the key quantity to determine the magic numbers.  相似文献   

13.
基于半经验的Gupta原子间多体相互作用势, 采用分子动力学方法并结合模拟退火及淬火技术, 系统研究了小尺寸铝团簇Aln (n=13–32)的熔化行为. 模拟结果表明: 除个别尺寸(Al13 和Al19) 外, 团簇熔化过程比热曲线普遍呈现杂乱无规(无明显单峰)现象, 这与实验观测小Al团簇比热普遍无规的结果完全一致. 通过分析不同温度点上团簇淬火构型的势能分布图给出了小Al团簇比热呈现无规或有规现象的成因. 对于比热无规团簇, 可以利用原子等价指数判断给出团簇熔点, 所得团簇熔点随团簇尺寸的变化趋势与实验观测结果完全一致. 关键词: Gupta势 团簇 分子动力学 熔化  相似文献   

14.
Heat capacities of small aluminium clusters A111-20 are investigated using MD simulation with empirical many- body Gupta potential. The heat capacities of some clusters A111, A112, A113 and A119 show well-defined peaks while the heat capacities of Alls-ls indicate a gradual melting transition. The spectra of isomers obtained by quenches along the MD trajectory give good interpretation for those results.  相似文献   

15.
The thermodynamics properties of noble metal clusters AuN, AgN, CuN, and PtN (N = 80, 106, 140, 180, 216, 256, 312, 360, 408, 500, 628, 736, and 864) are simulated by micro-canonical molecular dynamics simulation technique. The potential energy and heat capacities change with temperature are obtained. The results reveal that the phase transition temperature of big noble metal clusters (N ⩾ 312 for Au, 180 for Ag and Cu, and 360 for Pt) increases linearly with the atom number slowly and approaches gently to bulk crystals. This phenomenon indicates that clusters are intermediate between single atoms and molecules and bulk crystals. But for the small noble clusters, the phase transition temperature changes irregularly with the atom number due to surface effect. All noble metal clusters have negative heat capacity around the solid-liquid phase transition temperature, and hysteresis in the melting/freezing circle is derived in noble metal clusters.  相似文献   

16.
硅团簇熔化行为的紧束缚分子动力学研究   总被引:5,自引:0,他引:5       下载免费PDF全文
王坚  王绍青 《物理学报》2003,52(11):2854-2858
利用紧束缚分子动力学方法研究了硅团簇Sin(n=5—10)的熔化行为.给出了团簇 熔化潜热 和熔点随团簇尺寸的变化关系,表明团簇熔化潜热和熔点强烈依赖于团簇的原子数.计算结 果表明硅团簇熔化机理与金属团簇熔化有很大不同,金属小团簇的熔化是一个从低温类固态 向高温类固态转变的过程,在转变温区,类固态和类液态处于动力学共存,而硅团簇在转变 温区则是处于一种中间态,这种中间态既不是类固态又不是类液态.比较了用不同计算方法 和定义方法所得硅团簇熔点. 关键词: 紧束缚 硅团簇 熔化潜热  相似文献   

17.
The melting and freezing processes of CUN (N =180, 256, 360, 408, 500, 628 and 736) nanoclnsters are simulated by using micro-canonical molecular dynamics simulation technique, The potential energies and the heat capacities as a function of temperature are obtained. The results reveal that the melting and freezing points increase almost linearly with the atom number in the cluster increasing. All copper nanoclusters have negative heat capacity around the melting and freezing points, and hysteresis effect in the melting/freezing transition is derived in CUN nanoclusters for the first time.  相似文献   

18.
The thermodynamic and kinetic behaviors of gold nanoparticles confined between two-layer graphene nanosheets (two-layer-GNSs) are examined and investigated during heating and cooling processes via molecular dynamics (MD) simulation technique. An EAM potential is applied to represent the gold–gold interactions while a Lennard–Jones (L–J) potential is used to describe the gold–GNS interactions. The MD melting temperature of 1345 K for bulk gold is close to the experimental value (1337 K), confirming that the EAM potential used to describe gold–gold interactions is reliable. On the other hand, the melting temperatures of gold clusters supported on graphite bilayer are corrected to the corresponding experimental values by adjusting the εAu–C value. Therefore, the subsequent results from current work are reliable. The gold nanoparticles confined within two-layer GNSs exhibit face center cubic structures, which is similar to those of free gold clusters and bulk gold. The melting points, heats of fusion, and heat capacities of the confined gold nanoparticles are predicted based on the plots of total energies against temperature. The density distribution perpendicular to GNS suggests that the freezing of confined gold nanoparticles starts from outermost layers. The confined gold clusters exhibit layering phenomenon even in liquid state. The transition of order–disorder in each layer is an essential characteristic in structure for the freezing phase transition of the confined gold clusters. Additionally, some vital kinetic data are obtained in terms of classical nucleation theory.  相似文献   

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