H2O temperature ramp

Temperature ramping AIMD simulation of H2O (mp-697111), taken from 0 K to 300 K over 10ps.

Note on .cif visual above: bonding algo for our material visualizations are not so good. Will work on something better, or at least more configurable.

Experiment parameters

• MLIP model: M3GNet

• Friction: 0.1 / units.fs

• Time step: 1.0 * units.fs

• Steps: 15000 -> 15ps

• Temperature range: 0 K to 300 K

• Temperature ramp duration: 10ps

• Supercell: 3x3x3

• Total atoms: 324

Changed from previous simulation (NaCl):

• Increased friction from 0.01 / units.fs to 0.1 / units.fs

• Increased trajectory sampling rate, from 1 frame per 1000 steps to 1 frame per 100 steps

Trajectories

A little more action this time! Very cool to see the lattice pick up more energy and really start falling out of order. Next time, I'll just simulate right below freezing to right above freezing so we can watch the phase transition, if that works. By the end of the simulation here at 300 K, any resemblance of a crystal structure is gone and it's just free floating H20.

Also, I increased the trajectory sampling rate here so now each frame is 100 fs. Theoretically we can get 1 frame per femtosecond since that's our simulation step size, but we'll see how useful that much data actually is.

Watching the hydrogens on the oxygen is interesting too. They don't perfectly keep the 104.5 degree bond angle but instead move around quite a bit.

Temperature evolution

Steadier this time. It could be due to the increased friction which helped coupling between the environment and the material, but it could also be that this supercell was much larger. Around 300 atoms compared to around 50 for the NaCl simulation.

Trajectories file