Instantaneous Normal Mode Analysis of Liquids

Thomas Kyes得到了理论和计算化学计划的资助，继续他在液体的瞬时简正模式(INM)分析领域的研究。瞬时简正模式是液体典型构型的简谐模式，它们提供了对液体状态动力学的直观描述。凯斯将进一步发展INM理论来处理过冷液体中的弛豫。自扩散常数将由双势垒模计算出来，强过冷液体和脆性过冷液体的不同行为将与双势垒态密度的形式有关。过冷液体的其他性质，包括散射中的玻色子峰，可能增长的关联长度，关联函数的伸展指数衰减，斯托克斯-爱因斯坦定律的崩溃，以及空间非均质性的作用，将从INM计算出来。我们将研究当前理论的扩展，引入与时间相关的绝热和非绝热简正模处理。这将把INM治疗扩展到消相和运动性狭窄。已经有很好的理论模型来解释运动是混沌的、碰撞频繁且相互作用弱的气相系统的行为和性质。固态的理论模型也得到了很好的发展，因为晶体系统中的周期有序提供了必要的简化，从而导致了易于处理的解决方案。液体和过冷液体或玻璃的性质仍然对理论解释提出了相当大的挑战。凯斯是在发展液体物理和化学性质的分子解释方面取得重大进展的几位理论化学家之一。这项工作的长期影响可能在帮助理解凝聚相中的化学方面具有重要意义。

Thomas Keyes is supported by a grant from the Theoretical and Computational Chemistry Program to continue his research in the area of instantaneous normal mode (INM) analysis of liquids. Instantaneous normal modes are the harmonic modes of a representative configuration of a liquid, and they provide an intuitive description of liquid state dynamics. Keyes will further develop INM theory to treat relaxation in supercooled liquids. The self diffusion constant will be calculated from the double well modes and the distinct behavior of strong and fragile supercooled liquids will be related to the form of the double well density of states. Other properties of supercooled liquids including the Boson peak in scattering, a possible growing correlation length, stretched exponential decay of correlation functions, breakdown in the Stokes-Einstein law, and the role of spatial heterogeneity will be calculated from INM. An extension of the current theory will be investigated to introduce time-dependent adiabatic and diabatic normal mode treatments. This would extend the INM treatment to dephasing and motional narrowing. There are excellent theoretical models which explain the behavior and properties of gas phase systems where the motion is chaotic, collisions frequent, and interactions are weak. Theoretical models for the solid state are also quite well developed since periodic order in crystalline systems provides the necessary simplifications to lead to tractable solutions. The properties of liquids and supercooled liquids or glasses still present quite a challenge to theoretical interpretation. Keyes is one of several theoretical chemists who is making significant headway on developing a molecular interpretation of the physical and chemical properties of liquids. The long range impact of this work could be significant in helping to understand chemistry in condensed phases.