奈米水在石墨夾層間的結構與動力學

Abstract

在本論文中,藉由 LAMMPS 模擬器將被限制在石墨夾層間的 Extended simple point charge (SPC/E)模型之水分子做分子動力模擬,並研究在石墨夾層間距(h)從 7Å 到 20Å 間的奈米水系統中,水分子的局部結構及動力學。 模擬結果顯示,當 h 減小會使得石墨夾層間的水分子傾向於固體結構,且水分子 在垂直石墨牆方向上有分層現象。各水層的水分子分別在垂直、平行石墨牆方向 上皆會展現不同的運動行為。隨著 h 減小,各水層之氧原子的平移速度頻譜皆有 藍位移的現象。而在轉動頻譜的部分,當石墨夾層間距變窄,中間水層對於平行 氫氧鍵方向的轉動頻譜會出現兩個峰值,最接近石墨牆之水層的轉動頻譜則有藍 位移的現象。

In this paper, we performed molecular dynamics (MD) simulations by LAMMPS to study structural and dynamic properties of the extended simple point charge (SPC/E) model of water molecules confined between two graphite plates separated by at distance (h) 20, 15, 10 and 7Å. Our MD simulations indicate that nano-confined water shows layer structures parallel to the graphite plates and behaves more solid-like as the confined distance between graphite plates varies from 20 to 7Å. The water molecules belonging to different layers have various dynamical behaviors in the direction parallel or perpendicular to the graphite plates. By decreasing h from 20 to 7Å, a blue shift in the power spectrum of velocity autocorrelation function of oxygen atoms was observed in all water layers. In the direction parallel to an OH-bond, the power spectrum of the angular velocity autocorrelation function shows two peaks for water molecules in the central layer within the two graphite plates, and a blue shift for molecules in the layers closest to the graphite wall.