Tutorial_4_LJ10_opt

Tutorial_4_LJ10_opt - Oscar Tutorial 4 page 1 Tutorial 4:...

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Oscar Tutorial 4 page 1 Tutorial 4: Lennard-Jonesium The Search for the Global Energy Minimum in Two and Three Dimensions You may work alone or in a group of 2-3 people. Every student will try various methods of optimizing the structure of Lennard-Jonesium. You will prepare two reports, one for the two-dimensional case and one for the three-dimensional case. You may try any of the following algorithms: Energy minimization Molecular dynamics (MD) at constant temperature Monte Carlo (MC) at constant temperature Simulated annealing with MD Simulated annealing with MC You may choose any temperature protocol, by which I mean that you may use any constant temperature, or you may use any thermalization protocol you like. Note that, when you are running molecular dynamics, you may use any of the various algorithms for setting and maintaining temperature. Rule 1: All MD and MC simulations should be run for 10,000 steps or more. You can, of course, make test runs with fewer steps. Use whatever output frequency gets you the information you need. Rule 2: All final structures should be minimized to convergence, with a convergence criterion of 10 -15 , so we will all be comparing structures at similar stages of refinement. (Be sure you understand what “convergence” means!) Two Dimensions: The goal of this exercise is to determine the optimum method for finding the global minimum. To do this, you must answer two questions: Question 1 : How hard is it to find the global minimum starting from an arbitrary structure, using the algorithm (or algorithms) and the various protocols you tested? Question 2 : For your algorithm of choice, what was the best protocol you found? The goal is not to obtain the lowest energy structure, because we already know what that configuration is.
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Oscar Tutorial 4 page 2 Instructions: 1. Each member of your group should create his or her own initial structure, with all
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Tutorial_4_LJ10_opt - Oscar Tutorial 4 page 1 Tutorial 4:...

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