exercise_9

# exercise_9 - Molecular Dynamics Simulations 2011 Exercise...

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Unformatted text preview: Molecular Dynamics Simulations 2011 Exercise 9: Suggested solutions Eero Holmstr om November 16, 2011 1. In the spirit of last weeks exercise, we calculate the average volume of our system as a function of pressure. To simulate the system at P =- 5 ,- 4 ,- 3 ,- 2 ,- 1 , , 1 , 2 , 3 , 4 , 5 kbar, we use the script simulate_in_P_range : ./simulate_in_P_range -5 -4 -3 -2 -1 0 1 2 3 4 5 Then we employ calculate_average_V to get the average (thermalized) volume for each run: ./calculate_average_V -5 -4 -3 -2 -1 0 1 2 3 4 5 And again the P vs. V curve seems nearly linear, so we perform a first- order fit to get the derivative. From that, and the obtained volumes, we can calculate the bulk modulus: B =- V dP dV . (1) Using the default cut-off of 5 A gives us B 1187 kbar at P = 0 kbar, and using a longer cut-off of 8 A gives B 1396 kbar. The latter result in particular is very close to the experimental value of 1420 kbar, giving only a 2% error. This suspiciously good result can be explained by checking outa 2% error....
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## This note was uploaded on 02/14/2012 for the course CSE 6590 taught by Professor Kotakoski during the Winter '12 term at York University.

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exercise_9 - Molecular Dynamics Simulations 2011 Exercise...

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