多体互作用对13-原子团簇相变特性的影响

采用M.I.Baskes的Lennard-Jones Embedded-Atom(LJ-EMA)势作为原子之间的互作用,结合常能分子动力学模拟,计算了13-原子团簇的热曲线、方均根键长起伏、比热、动能的短时平均、位移平方的平均、其它12个原子相对于中心原子的角分布函数,着重地计算了相变区域的情形,对团簇融化-凝固相变特性进行了较为详细的研究,得出多体作用力的大小增加、范围减小导致融化温度(动能)的降低和共存区域范围变小的结论;证实了在一定的总能范围内类固(solidlike)和类液(liquidlike)两类特性团簇的共存;进一步明确了两步过程(表面融化)的成因;观察到在三种较大多体互作用范围势的情况下,出现负比热;进一步揭示了热曲线斜率、方均根键长起伏、比热和动能的短时平均分布之间的关联。

Influence of the Many-body Interaction on Cluster Phase Transition

Using a Lennard-Jones Embedded-Atom(LJ-EMA)potential proposed by Bakes,combined with the constant energy molecular dynamics simulation,we calculated the caloric curve,the rms bond length fluctuations,the specific heat,the short-time average of kinetic energy,the mean-square displacement,and the angular distribution function of a 13-atom cluster.The influence of many-body interaction on cluster phase transition was extensively studied,and particular attention was paid to the coexistence region.It was observed that increasing the magnitude or decreasing the range of the many-body leads to a decrease in the melting temperature;the coexistence of a solidlike form and a liquidlike form within certain range of total energy was confirmed;the origin of a two-step cluster melting process was further elucidated;the correlation of the slope changes of caloric curve,the rms bond length fluctuations,the evolution of specific heat and the short-time average of kinetic energy was opened out;the fact of negative specific heat was found when three potentials of having larger interaction ranges were used.