A Comparison of Force-Field models for Nanotube Mechanics
John Karspeck-Colorado State University
Sound
and Vibration REU
Funded by the Army Research Office and the National Science Foundation
|
C24: Carbon molecule with Hydrogen bonded ends
BN24: Born Nitride molecule with Hydrogen bonded
ends
An energy profile for
Cerius2. The lowest Energy point is taken to be the value of Poisson’s Ratio. |
Ab
initio software is often used to find the properties of inorganic nanotubes.
Ab initio uses quantum mechanics to calculate the energy of the structure.
While the most accurate, ab initio calculations are very time consuming. In
order to enable faster calculations molecular mechanics software can be used.
Molecular mechanics calculates the structures energy by measuring the bond
stretch, bend, torsion. These energies are then summed into what is called a
Force-Field; this is the relative energy of the structure. The problem with
molecular mechanics is the calculations depend on bond information and other
parameters. The model often has to be adjusted in order obtain accurate
calculations. This
summer’s research included finding Young’s Modulus, Poisson’s Ratio, and the
effective thickness of small Carbon and Boron Nitride molecules. These were
found using several molecular mechanics packages: Allinger’s mm2, Cerius2,
and apt. The properties obtained from these calculations were compared to the
ab initio calculations. This will assist in determining what adjustments must
be made to the Force-Field in order to run larger sheets. Results
For C24:
Collaborators: Dr.
Paul Heyliger Dr.
Anthony Rappé Mr. Fernando Ramirez |
