Simulation and Theory of Solid-Liquid Interfaces and Grain Boundaries

堪萨斯大学的布莱恩·莱尔德得到了理论、模型和计算方法项目颁发的奖项的支持。该项目的重点是了解原子和分子相互作用在塑造固体-液体和固体-固体界面的热力学和动力学性质方面所起的作用。这项工作需要开发、评估和应用新的计算方法。所提出的方法是使用模型势对界面的基础研究和对现实材料的研究的混合。界面现象的可靠实验结果是具有挑战性的，也是罕见的。因此，原子模拟是确定这类过程热力学唯象的重要手段。凝聚态系统中界面的热力学和生长动力学主要由两个量控制：界面自由能和动力学系数。两个共存相之间的界面自由能是可逆地形成单位面积界面所需的功。动力学系数是推进界面的生长速度与过冷温降之间的比例常数。为了充分理解树枝状晶体生长、晶体成核、润湿、液态金属脆化等现象，两者的准确数值是必要的。将解决的具体任务是：(I)量化界面自由能对原子和分子相互作用的依赖的新方法，(Ii)计算晶界自由能的直接方法发展，(Iii)研究化学非均相固-液界面的界面热力学和结构的方法适应，(Iv)检测动力学系数对分子间力的依赖的方法，以及(V)计算包括二元混合物在内的分子系统的界面自由能的方法。更广泛的影响包括继续参加材料科学家、化学家和物理学家之间每半年举行一次的材料界面动力学和凝聚力合作研究小组。对学生进行计算化学、编程和建模技术培训的努力将在堪萨斯大学化学NSF资助的REU项目中进行，该项目有很强的代表不足群体参与的历史。

Brian Laird of the University of Kansas is supported by an award from the Theory, Models and Computational Methods program. The project focuses on understanding the role that atomic and molecular interactions play in shaping thermodynamic and kinetic properties of solid-liquid and solid-solid interfaces. This effort requires development, evaluation and application of new computational methods. The proposed methodology is a mixture of fundamental studies of interfaces using model potentials with studies of realistic materials. Reliable experimental results of interfacial phenomena are challenging and rare. Thus, atomistic simulation is an important means for determining the thermodynamic phenomenology of such processes.The thermodynamics and growth kinetics of interfaces in condensed matter systems are primarily controlled by two quantities: the interfacial free energy and the kinetic coefficient. The interfacial free energy between two coexisting phases is the amount of work required to reversibly form a unit area of interface. The kinetic coefficient is the constant of proportionality between the growth velocity of an advancing interface and the undercooling drop in temperature. Accurate values of both are necessary for the full understanding of phenomena such as dendritic crystal growth, crystal nucleation, wetting, liquid-metal embrittlement, and others. Specific tasks that will be addressed are: (i) new method to quantify the dependence of the interfacial free energy on atomic and molecular interactions, (ii) direct method development to calculate grain boundary free energies, (iii) method adaptation to study the interface thermodynamics and structure of chemically heterogeneous solid-liquid interfaces; (iv) method for detecting the dependence of the kinetic coefficient on intermolecular forces, and (v) method to calculate the interfacial free energy of molecular systems, including binary mixtures.Broader impacts include continued participation in a cooperative research team on Dynamics and Cohesion of Materials Interfaces encompassing semiannual collaborative meetings between materials scientists, chemists and physicists. Efforts for training of students in the techniques of computational chemistry, programming and modeling will be undertaken within the Chemistry NSF-funded REU program at Kansas University, which has a strong history of participation by underrepresented groups.