Thrust 2

Thrust 2 - Computational prediction of synthesis pathways. 

(Zhang (Leader), Li, Xia, Ye, Moraru, Wang, Yao, Richard)

This thrust develops and executes exascale workflows to efficiently acquire thermodynamics data and phase selection/nucleation kinetics. The goals are to understand the local energy landscape between transient or intermediate products, and to guide precision synthesis by suggesting synthesis pathways. Currently, many computational predicted new compounds cannot be synthesized, largely due to a lack of knowledge about the necessary synthetic pathways. We leverage a molecular dynamics (MD) simulation package, LAMMPS, an Exascale Computing Project (ECP) code supported by DOE, and incorporate several robust and powerful computational methods and tools developed at Ames National Laboratory (Ames Lab) , to substantially speed up the prediction of synthesis pathways for complex functional materials. Accurate and efficient ANN-ML interatomic potentials are developed to ensure reliable and efficient MD simulations of complex materials.

The phase diagram based on precise free energy calculations provides essential guidance for materials synthesis. The thermodynamic integration (TI) technique is highly accurate for free energy calculations, yet it is also resource-demanding. For instance, hundreds of MD jobs are required to map out the free energy of a binary solution phase (such as liquid) as a function of temperature (T) and composition (x). We have set up a framework that uses Parsl, an open-source Python library for parallel programming, to efficiently manage the MD jobs according to the available resources. Fig. 2 (a) shows almost ideal strong scaling of this framework for the calculation of the free energy of the Al-Sm liquid in the Al-rich regime (x_sm <= 0.25) based on an EAM potential. Fig. 2 (b) gives the resulting mixing Gibbs free energy G_mix(x,T) of Al-Sm liquid referenced to the two end compositions: pure Al liquid and Al_0.75Sm_0.25 liquid.  The free energy of Al-Sm liquids and the two competing solid phases fcc-Al and Al₃Sm can be used in CALPHAD modeling to obtain the melting line shown as the red curve in Fig. 2(b).