Sehgal Ray M, Maroudas Dimitrios, Ford David M
Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Chem Phys. 2014 Mar 14;140(10):104312. doi: 10.1063/1.4866810.
We have developed a coarse-grained description of the phase behavior of the isolated 38-atom Lennard-Jones cluster (LJ38). The model captures both the solid-solid polymorphic transitions at low temperatures and the complex cluster breakup and melting transitions at higher temperatures. For this coarse model development, we employ the manifold learning technique of diffusion mapping. The outcome of the diffusion mapping analysis over a broad temperature range indicates that two order parameters are sufficient to describe the cluster's phase behavior; we have chosen two such appropriate order parameters that are metrics of condensation and overall crystallinity. In this well-justified coarse-variable space, we calculate the cluster's free energy landscape (FEL) as a function of temperature, employing Monte Carlo umbrella sampling. These FELs are used to quantify the phase behavior and onsets of phase transitions of the LJ38 cluster.
我们已经开发出一种对孤立的38原子 Lennard-Jones 团簇（LJ38）相行为的粗粒度描述。该模型既捕捉了低温下的固-固多晶型转变，也捕捉了高温下复杂的团簇分解和熔化转变。对于这种粗粒度模型的开发，我们采用了扩散映射的流形学习技术。在较宽温度范围内进行的扩散映射分析结果表明，两个序参量足以描述团簇的相行为；我们选择了两个合适的序参量，它们是凝聚和整体结晶度的度量。在这个有充分依据的粗变量空间中，我们采用蒙特卡罗伞形抽样计算团簇的自由能景观（FEL）作为温度的函数。这些FEL用于量化LJ38团簇的相行为和相变起始点。
