I want to build amorphous Al$_2$O$_3$ with the AIMD (ab-initio molecular dynamics) method implemented in VASP. I know that two procedures should be taken into account, namely
- 1st: melt
- 2nd: quench
Following this workflow, I encounter some questions as follows:
How big should the melt supercell take?
The conventional cell of Al$_2$O$_3$ is taken from the materials project website, in which it contains 15 atoms, as shown in the following figure.
To do AIMD calculations, we must contain enough atoms in the simulated cell. It means that I need to build a supercell. For the current system, a $3 \times 3 \times 1$ (135 atoms) supercell is OK? To obtain a reasonable amorphous structure, how big the melt supercell should take?
Once the supercell is built, I need to heat the supercell to melt it.
How to take the beginning temperature (TEBEG=X1) and ending temperature (TEEND=X1)? How to set the timestep (POTIM=X2 fs) and simulation numbers (NSW=X3)?
If the previous two questions are solved, I have a melting structure. Now I need to quench the structure to obtain the amorphous structure, also by doing AIMD.
How to set the beginning temperature (TEBEG=X1) and ending temperature (TEEND=X5)? How to set the timestep (POTIM=X2 fs) and simulation numbers (NSW=X3)? How to judge the final structure?
If the workflow is wrong, please help me to correct it.
Many thanks in advance.