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Anyway, I am a first year grad student working on molecular dynamics simulations (with very little background in materials, yay) of iron. To start out, I'm just trying to replicate some materials constants with a basic lattice to make sure things are going well...

I want to calculate the energies of formation of interstitial dumbbells in various directions, <100>, <110>, <111>... I set up a perfect iron lattice, 10x10x10, and find it's total energy (-8244.8702 eV). Then, I insert an interstitial in the lattice inside one of the cubes (it's bcc iron), near where it's position would be for a <110> dumbbell, and let it run for about 100 timesteps to relax into a stable position. This is all at 0 K, by the way, and an NVE constant simulation. Now looking at the total energy, I have (-8141.51). I had thought that the magnitude of the energy should be higher with an interstitial, but it's not... so does anyone have an explanation for that, or a formula to calculate energy of intersitial formation?

I thought it would be analogous to the energy of vacancy formation equation (which I calculated fine), but doesn't seem to be... thanks