Determine how the timing of a calculation changes with the size of the molecule

Determine how the timing of a calculation changes

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7.Determine how the timing of a calculation changes with the size of the molecule. First draw the following, CH3(CH2)nCH3, where n varies from 0 to 15. Then run “Comprehensive Cleanup” while in the Builder screen. Run single point energies for these polymers using PM3. After this, perform the same operation using HF for n = 0 to 5. Plot up the timings as a function of polymer size. How do the two methods compare? At what size do you expect the polymer to take unreasonably long to converge? n PM3 (Hartree) HF(Hartree) 0 -0.02735 -79.22 1 -0.03537 -118.26 2 -0.04319 -154.30 3 -0.05100 -196.33 4 -0.05881 -235.36 5 -0.06663 -274.40 6 -0.07444 n/a 7 -0.08225 n/a 8 -0.09007 n/a 9 -0.09788 n/a 10 -0.1057 n/a 11 -0.11351 n/a 12 -0.12133 n/a 13 -0.12914 n/a 14 -0.13695 n/a 15 -0.14477 n/a 0 0.1 0.2 0.3 0.4 0.5 0.6 0 2 4 6 8 10 12 14 16 Time (seconds) n PM3
The energy for PM3 is lower in magnitude compare to HF. The time it takes to converge compared to n is steady only increasing by 0.1 seconds after n=12 using PM3. It increases rapidly using HF. It will take a molecule that is greater than n=15 to take unreasonably long to converge using PM3. Looking at the trend of the graph of PM3 the molecule must be very great in size because even at n=15 it only took 0.5 seconds. Using HF, a molecule of n=15 might take an unreasonably long to converge according to the trend of the graph. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 Time (seconds) n HF

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• Summer '20