Computing Melting Point by Free Energy Method

Computing Melting Point by Free Eneregy Method

Seunghwa Ryu and Wei Cai

This tutorial describes how to compute melting points from free energy methods. We provide the MD++ script files and describe how to use them in detail. The theoretical background is published in

Comparison of Thermal Properties Predicted by Interatomic Potential Models, Modelling and Simulation in Materials Science and Engineering, 16, 085005 (2008). (PDF).

Download files

First, you need to install MD++ on your computer by following the instructions on MD++ Manuals.

Second, copy files melting_cubic.tcl and melting_noncubic.tcl to your input file directory of MD++. You can do so by

 mkdir -p ~/Codes/MD++/scripts/work/melting
 cd ~/Codes/MD++/scripts/work/melting
 wget http://micro.stanford.edu/mediawiki-1.11.0/images/Melting_cubic.tcl.txt -O melting_cubic.tcl
 wget http://micro.stanford.edu/mediawiki-1.11.0/images/Melting_noncubic.tcl.txt -O melting_noncubic.tcl

Both files contain a big comment section in the beginning that describes in detail the (16) steps to computing melting point. These steps are fully automated. In this tutorial, we describe how to run these scripts on a parallel cluster (using wcr.stanford.edu as an example) and what kind of results you should expect.

Submit jobs

Here are the PBS scripts for submitting the jobs on wcr.stanford.edu.

Analyse data

At the end of the calculation, data files and Matlab files will be automatically generated. Transfer these files to a location where you have Matlab installed. Run the following commands in Matlab and you will get the free energy plot (for solid and liquid phases). The melting point is the temperature at which the two free energy curves cross.