Posted in D L Williams, Education, Physical Chemistry

This Week in Pchem – Energy Minimization Techniques

This week in pchem we are discussing the energy minimization techniques that are used in computational chemistry. The students will build a mock energy function that models the dihedral rotation of 1,2-dichloroethane. Then three methods (The Monte Carlo Method, Newton minimization, and Metropolis simulated annealing) will be employed to solve for the preferred (lowest energy) dihedral angle (a).   

A performance plot will also be generated that shows the lowest energy and its root mean squared deviation RMSD from the known minimum structure (a = 180 degrees).  This plot clearly shows Newton’s propensity to get stuck in local minima.  It also clearly shows that the Monte Carlo method will always find the global minimum, but with increasing inefficiency.  And finally, the Metropolis simulated annealing technique is found to be flexible enough to accurately locate the minimum energy structure every time provided that the step size and temperatures are “tuned”. 

Stay “tuned” for a planned video of the spreadsheet in action.

You can participate!  Download the Rosetta@home screen saver, and solve protein folding problems in your sleep.  (I have no official connection to the Rosetta at home folks, but their work is great! http://boinc.bakerlab.org/rosetta/)

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Author:

Dr. Darren L. Williams (pchem4u) is an Associate Professor of Physical Chemistry at Sam Houston State University. When he is not blending solvents, he is tinkering with contact angle measurements, FTIR microspectroscopy, etc. http://www.shsu.edu/~chm_dlw/ . He welcomes your comments and questions by phone (936-294-1529) and by email (williams “at” shsu.edu).

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