[lammps-users] Is minimize command invalid to periodic boundary conditions (PBC)

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1

Dear all,

Here is a problem about the minimize command. I would like to study the equilibrium lattice structure under a given pressure (uniaxial compression, biaxial compression, etc). First I make some deformation to the crystal which is equivalent to applying strain or stress. Then I use steepest descent (SD) algorithm to minimize the system energy. However, I found that the minimization will be finished only after one or two step with the system energy almost unchanged, such as the potential energy, the lattice constant. One point should be noticed that I have used periodic boundary conditions (PBC) in all the three directions.

Thus, I wonder whether minimize in SD method will be invalid to PBC.

Could I complete the minimization process to adjust the lattice structure, such as the change of crystal volume or shape, etc, under a given pressure?

Best regards,
Suzhi Li

2

If your atoms are on a perfect lattice, even under compression, then
they're in a local minimum, and doing a SD or CG minimize won't
change them. If you want to couple box size/shape changes to
your minimization then you should use fix box/relax with your minimize.

Steve