液態鎵熱力學及結構之研究

Abstract

最近，由Mansoori-Canfield/Rasaiah-Stell(MCRS)用硬球流體做參考系統所推導的熱力學微擾理論已被修正，而修正項是由於部分相空間為硬球流體所禁止。由非常軟的粒子所構成液體的額外Helmoholtz 自由能，利用此修正的MCRS理論計算時，發現非常精確。在液態鎵內，兩鎵離子間的作用力包括短程的斥力與長程的Friedel振盪位能。此計劃的第一部份，將利用此修正的MCRS理論計算液態鎵的熱力學函數，其一目的是用液態鎵的位能模型檢驗此理論。 導致於短程的斥力與長程Friedel振盪位能的交互作用，液態鎵的特殊結構表現於靜態結構因子的主峰較大波數的一側有一突出的肩膀。從微觀結構的觀點，此特殊結構被提議是與固體似的叢集的出現有關。當鎵由液態被降溫至非晶態或晶體時，此固體似的叢集變為主要結構。此計劃的第二部份，我們將用局限性方向鍵結參數確認此固體似的叢集，若其存在的話。

Recently, the thermodynamic perturbation theory, derived by Mansoori-Canfield/Rasaiah-Stell （MCRS）with the hard-sphere (HS) fluid as the reference system, has been generalized by including a configuration integral correction, which is associated with the forbidden region in the phase space of the HS fluid. The excess Helmoholtz free energy predicted by the extended MCRS theory is found to be accurate for the fluids with the inverse-power potential, which has a very soft repulsive core. In the first part of the project, we will calculate the thermodynamic properties of liquid Ga by the extended MCRS theory, with an aim to test the theory with the interatomic pair potential, which has a ledge-shape repulsive core and the long-range Friedel oscillations. Resulted from the interplay between the ledge-shape repulsive core and the long-range Friedel oscillations, the peculiar structure of liquid Ga exhibits a shoulder on the high-wavevector side of the first peak in the static structure factor. From the view point of local structures, the peculiar structure is proposed to be associated with the appearance of some solid-like clusters, which becomes predominated as liquid Ga is quenched into the amorphous states and -phase crystal. In the second part of the project, we will identify the solid-like clusters, if exists, with the local bond-orientational order parameter.